Capacitive touch screen stylus

ABSTRACT

In some embodiments, a stylus for providing input to a capacitive touch screen, having a tip including or consisting of conductive felt, which provides a deformable conductive surface for contacting the touch screen. The tip is produced by felting base fibers (which are typically non-conductive) with conductive fibers. In other embodiments, a capacitive touch stylus having at least a first mode of operation and a second mode of operation, and including at least one conductive tip and switched circuitry (preferably, passive circuitry) including at least one switch biased in a default state indicative of the first mode of operation but switchable into a second state indicative of the second mode of operation in response to movement of the tip (typically, in response to exertion of not less than a threshold force on the tip). In some embodiments, a stylus having a conductive tip (e.g., a conductive, felted tip) and including switched circuitry (preferably, passive circuitry) having a first state which couples a capacitance to the tip, where the capacitance is sufficient to allow a capacitive touch screen device to recognize (as a touch) simple contact of the tip on the screen of the touch screen device, and a second state which decouples the capacitance from the tip, thereby preventing the touch screen device from recognizing (as a touch) simple contact of the tip on the screen.

RELATED APPLICATION

The present application claims the benefit of U.S. ProvisionalApplication No. 61/353,788, filed on Jun. 11, 2010, by Paul Anson Brownand titled “Capacitive Touch Screen Stylus with Deformable Felted Tipand/or Passive Switched Circuitry for Indicating Mode.” U.S. ProvisionalApplication No. 61/353,788 is hereby incorporated by reference herein inits entirety.

FIELD OF THE INVENTION

The invention pertains to a stylus for use as an input device for acapacitive touch screen and to systems including a stylus and a touchscreen device configured to register and to recognize touches of thestylus tip on the touch screen. In an embodiment, the touch screendevice includes communication ports (e.g., Bluetooth, USB, RS232, anaudio input port, etc.) and a processor coupled to the communicationport and to the touch screen, and the stylus includes switched circuitryfor communicating stylus events to the processor through thecommunication port.

BACKGROUND OF THE INVENTION

The expression “switched circuitry” is used herein to denote circuitryincluding at least one switch. The switched circuitry may be part of acomplete circuit (through which current can flow only when said part iscoupled to another part of the circuit) or it may be a complete circuit(through which current flows when each said switch is in a stateallowing the current to flow). An example of “switched circuitry” is aset of circuit elements connected in series, where at least one of theelements is (e.g., all of the elements are) included in a stylus, theelements include a switch that is selectively switchable between aclosed state and an open state. In an embodiment, the switch isselectively switchable in response to externally applied force e.g., aswitch biased in an open state and configured to enter a closed state inresponse to application of sufficient force on the switch, or a switchbiased in a closed state and configured to enter an open state inresponse to application of sufficient force on the switch, and theswitch's state is indicative of a mode of operation of the stylus.Passive switches may also be included.

The term “conductive” is used herein to denote “electricallyconductive.”

The expressions “touch screen device” and “touch screen” are used hereinas synonyms to denote either a capacitive touch screen or a device(e.g., a portable computing device or handheld phone) that includes acapacitive touch screen. This term is also intended to refer to screensthat use projected capacitive touch technology. (“PCT.”) A “touch screendevice” (or “touch screen”) includes a screen intended to be touched byhuman fingers and/or styli and a system for recognizing touches (andstrokes) on the touch screen by objects. A “touch screen device” (or“touch screen”) may include a computing system (sometimes referred toherein as a “processor”) configured to display images on the screenand/or perform other operations in response to recognized touches orstrokes on the screen. A “touch screen device” or “touch screen” mayalso include other subsystems e.g., an audio subsystem including atleast one audio input port and at least one audio output port, andconfigured to assert output an audio signal at each audio output portand to receive analog audio at each audio input port and to generatedigital audio data by sampling the received audio.

Capacitive and PCT touch screens have become ubiquitous in handheldphones and computing devices. These touch screens present uniquechallenges for the design of styli that can serve as input devices tothem. It is problematic to use a stylus as an input device for acapacitive touch screen originally designed for actuation based on thecapacitive coupling of a human finger, for several reasons including thefollowing:

the stylus must mimic the capacitive load of a human finger and providea coupling area sufficient for the touch screen circuitry to be fooledinto responding as if to the contact of a human finger;

the stylus tip must provide capacitive coupling approximate to thecapacitive coupling of a human finger. This usually means that the tipmust itself be a conductive surface. The stylus tip also should notscratch the surface of the touch screen. Conductive, deformable,non-scratching, low friction, inexpensive materials present a uniquedesign challenge; and

capacitive touch screens technologies often use a high precision glasspane that provides the contact surface for the human finger. To use astylus on this smooth glass surface, one must have a stylus tip that iscapable of creating a coupling point that is large enough to meet a twodimensional minimum contact area that allows the touch screen tocalculate a centroid from the outline of the contact area.

Conventional proposals for solving this problem are sub-optimal, and usestylus tips that:

(A) provide a deformable or pliable surface (typically a conductivesurface of hemispherical or conical shape when not deformed), comprisean elastomeric (or flexible polymeric) material that is either bare orcovered by a conductive (or thin, non-conductive) layer, and aredeformable when pressed against a touch screen to contact a region ofthe screen having sufficiently large area for recognition by the touchscreen device (see, for example, US Patent Application Publication Nos.2008/0297491 A1 and 2009/0262637A1); or

(B) include an articulated disk or semi-flattened sphere on a ball jointthat provides a two-dimensional coupling area that meets the minimumrequirement (see, for example, US Patent Application Publication Nos.2010/0006350 A1 and 2009/0211821 A1); or

(C) consist of a mass of metal wires (see, for example, US PatentApplication Publication No. 2008/0297491 A1) or include a cover ofconductive fabric containing conductive wires over a flexible,conductive region (see, for example, US Patent Application PublicationNo. 2009/0262637A1).

Styli that employ method (C) are sub-optimal since a stylus tip surfaceof metal wires (or conductive fabric containing wires) would be abrasiveand tend to scratch or abrade a touch screen surface.

Styli that employ method (A) are sub-optimal since any elastomer actslike a spring, and elastomeric or flexible polymeric material havinghemispheric (or conical or similar) shape sliding on a touch screen hasan increased coefficient of friction as the material deforms in responseto being pressed against the screen (to provide a sufficiently largetwo-dimensional coupling surface area with the screen). The increasedcoefficient of friction (especially when it is due to a deformedelastomer that exerts spring force on a touch screen against which it ispressed) impedes the glide of the stylus tip across a touch screen, thusmaking it more difficult for the user to write or draw with the touchscreen device. An elastomeric stylus tip covered with a conductive wiremesh (e.g., as disclosed in US Patent Application Publication No.2008/0297491 A1), or a stylus tip comprising a pliable cover (e.g.,conductive fabric containing conductive wires, or elastomeric or plasticmaterial embedded with conductive material, or thin non-conductivematerial) over conductive, elastomeric (or polymeric), flexible material(e.g., as disclosed in US Patent Application Publication No.2009/0262637A1), is not immune to problems due to increased coefficientof friction with increasing deformation. The level of friction betweensuch a conventional stylus tip and a touch screen requires a designbalance in which the designer must either choose to make the material incontact with the screen soft enough to prevent the glass surface frombeing abraded over time versus making the tip material durable enough tolast a long time. It had not been proposed before the present inventionto provide a capacitive touch screen stylus with a tip of conductivefelted material (comprising non-conductive fibers felted with conductivefibers) to reduce or eliminate conventional touch screen stylus problemsin due to undesirable levels of friction and abrasiveness.

Styli that employ method (B) have the problem that the disk requires apivot point that increases cost and fragility of the device.Furthermore, as the disk makes contact with the touch screen when usedas a writing implement it is unreasonable to assume that the user willalways keep the disk perfectly parallel to the plane of the touch screenwhen raising and lowering the stylus tip, thus provoking an incorrectcentroid calculation during the time between the edge of the disk makingcontact and the full disk area seats onto the plane of the glasssurface. This would result in an unintentional user stroke to berecorded by the device.

It would be desirable to implement a stylus as an input device for acapacitive touch screen in a manner that overcomes the limitations anddisadvantages of conventional styli intended for use for this purpose.

Capacitive and PCT touch screens are typically optimized for use withhuman fingers. However, humans have spent a considerable amount of timebuilding dexterity to write using a stylus pen or pencil. Writing ordrawing with a finger is cumbersome and difficult. Conventionalcapacitive touch screens typically operate with host software (e.g., arecoupled to processors programmed to execute host software) thatrecognizes gestures of single or multiple touches on the screen. Whenusing a stylus as an input device for a conventional touch screen,problems due to unintended touches on the screen can arise. A naturalway to write on any surface with a stylus (e.g., pen or pencil) involvesresting the base of the hand as a fulcrum and using the thumb and otherfingers to guide the movement of the stylus. Given a large enough touchscreen, the base of the user's hand (as well as the stylus) touches thescreen during writing.

The inventor has recognized that an important problem to be addressed inorder to use a stylus as an input device for a capacitive touch screendevice (sometimes referred to herein as the “disambiguation problem”) ishow to allow the touch screen device (sometimes referred to herein as a“host device”) to distinguish between a user-intended stylus tip touchon the screen, and an unintended touch on the screen (e.g., a touch onthe screen by a user's hand gripping a stylus, or another object that isnot the stylus tip, which is not intended to provide input to the touchscreen device). The touch screen device (e.g., host software running onthe device) must disambiguate intended writing (or other input strokesor touches) from unintended touches (e.g., by the base of the user'shand) to provide stability. It would be desirable to implement a stylusand/or host device in a manner that addresses the disambiguation problemin an efficient and inexpensive manner (e.g., without unacceptable costand complexity in design and manufacture of the stylus, and preferablywithout requiring that the host device include any hardware that is nottypically included in a conventional version of the host device).

A capacitive touch screen device typically must be able to recognizewhether a touch on a screen is a finger touch or a stylus touch. Aconventional proposal for achieving this (described in above-cited USPatent Application Publication No. 2010/0006350 A1) uses a poweredstylus equipped with sensors and switches for selecting modal data to beasserted to the touch screen device via wireless communication and/ordirect stimulation of the capacitive touch screen.

BRIEF DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In a first class of embodiments, the invention is a stylus for providinginput to a capacitive touch screen. The stylus has a tip comprising(i.e., consisting of) conductive felt, which provides a deformableconductive surface for contacting a touch screen (with a sufficientlylarge contact area to allow the touch screen to recognize a touch by thetip). Typically, the tip is sufficiently smooth to be capable of beingmoved in contact with the touch screen with less than an undesirableamount of friction (between the tip and touch screen surface in contacttherewith), in the sense that a user who moves the stylus on the screento write with the stylus feels no more friction (between the stylus andthe screen surface) than is typical during writing with a conventionalpencil or pen on paper. The tip comprises first fibers (which aresometime referred to herein as “base” fibers, and are typicallynon-conductive) and conductive fibers, and is produced by felting thebase fibers with the conductive fibers using the fiber materialtechnique commonly known as felting. The base fibers are selected to beconducive to felting (i.e., to have properties at the microscopic levelthat allow them to bond and tangle with one another in the presence ofwater and agitation), and to have sufficient smoothness to producesufficiently low friction when used (after being felted) as a capacitivetouch screen stylus tip, and preferably to have low cost. During thefelting process, the base fibers capture the conductive fibers andthrough specific felting techniques form an at least substantiallyspherical or hemispherical felt object (or a felt object of other shape)that is semi-rigid (in the sense in the sense that it retains its shapeunless and until it is deformed by forcing it against a touch screen orother object), and can be mounted to a distal end of a support to form astylus. In use of the stylus, the felt object functions as a conductivestylus tip that couples a sufficient capacitance to a touch screen, at acontact region on the screen of sufficient area, to allow recognition ofa touch by the tip.

The technique for manufacturing typical embodiments of the stylus tipstarts with a base fiber (preferably a common, inexpensive base fiber)that is already conducive to felting. Wool or any other fiber that hasscales which interlock at the microscopic level during a felting processis suitable as a base fiber in many embodiments. Interspersing this basefibers with conductive fibers, which typically do not have the samemicroscopic characteristics necessary for felting, allows the basefibers to lock and hold the strands of the conductive fibers. Thefelting should produce a semi-rigid, felt object having shape suitablefor use as the tip of a capacitive touch screen stylus (e.g., spherical,hemispherical or bullet-like shape), and size suitable for affixing tothe end of a capacitive touch screen stylus body (e.g., a conductive rodor tube, or a non-conductive tube including or coupled to a capacitance,where the capacitance is connected by a conductor to the felt object inat least one operating mode). When the stylus has a conductive body, theconductive body (and optionally a conductive structure between the felttip and the conductive body) couples with the human hand and thereforeprovides a low impedance path between the conductive felted tip and thehuman body, allowing a capacitive touch screen to properly calculate acentroid based on the area of contact between the tip and the screen. Byusing base fibers of sufficiently low friction (when felted) in the tip,the coefficient of friction of the felted tip against the glass surfaceof a capacitive touch screen is significantly low to allow for a natural(pen-like) feel of the stylus as the tip slides on (or is touchedagainst) the screen.

The blending percentage of the conductive fibers and diameter of thefelted tip can be chosen to be optimal for the intended use of thecapacitive touch screen stylus. The minimum capacitive load to becoupled via the tip, and the minimum two-dimensional contact area of thetip with the screen, will depend on the host device with which thestylus is used. The conductive fibers can be any fibers that inherently(or are modified to) have electrical resistivity preferably less than10,000 ohms-cm (and not more than on the order of 10,000,000 ohms-cm).To produce the tip, the base and conductive fibers are mixed in a ratiosufficient for the tip to have sufficient conductivity to provide theelectrical coupling necessary for a stylus including the tip tostimulate a capacitive touch screen. The tip's conductive fibers (ratherthan any other element of the tip) provide the tip's conductivity thatis required for its intended use (e.g., the conductive tip is normallyused when dry, but even if it happens to be used when wet with aconductive liquid or contaminated with a conductive substance, it doesnot rely on the liquid's or the contaminant's conductivity to be usefulas a capacitive touch screen stylus tip).

Examples of conductive fibers suitable in typical embodiments includebut are not limited to carbon fibers, fibers coated with metal, andfibers coated with carbon. The exemplary conductive fibers havelow-friction and non-abrasiveness properties similar to those of typicalbase fibers with which they are felted. Thus, when felted with the basefibers to produce a stylus tip, the tip can have acceptably low frictionand non-abrasiveness. In contrast, metal wires are typically moreabrasive than the exemplary conductive fibers. Thus, a tip consisting(or including a significant quantity) of metal wires would typicallyabrade the surface of a touch screen during use.

In some embodiments, the tip comprises 1/3 conductive fibers and 2/3base fibers. The conductive fibers may comprise Jarden materialsRESISTAT® TYPE F9216, merge L040, nylon electrically conductive withcarbon suffused onto the fiber surface, cut into 4 inch lengths andhaving a resistance of 4000 ohm/cm. The base fibers may comprise 18.5micron Merino wool fibers. In this instance, 0.06 grams total materialfelts into a ball approximately 0.250″ in diameter. The weight isapproximately 0.05 grams per piece. A 1/16″ diameter brass rodapproximately 1.85″ long may be utilized as support structure for thetip. The tip may be constructed by mixing the wool base fiber with theconductive fiber using a drum carder to achieve uniform mixing. Thematerial is weighed and separated into 0.06 gram amounts. Balls are spunin a toroidal shaped grooved mold with a standard hand drill @ 1000 RPMunder hot tap water utilizing Dr. Bronner's soap as a lubricant. Theballs are then left to air dry. The air dried balls are then drilled 50%through and the brass rod is inserted into the resulting hole andaffixed utilizing standard 5 minute epoxy.

In some embodiments, the above-mentioned conductive and base fibers aremixed according to the 1/3 conductive fiber, 2/3 wool fiber ratio. Themixture strands are then felted into a cord by adding water and soap andhand rolling and stretching the cord to achieve a uniform cylinder witha circular cross-section. The cylindrical diameter may be ⅛″. Thestrands are then cut into desired lengths, e.g. 0.25″. The brass rod isthen inserted into the center of one circular face of the cylinder andepoxied into place utilizing, for example, standard 5 minute epoxy. Theother circular face of the cylinder may then be trimmed to provide ahemispherical end to the cylinder to make the tip structure “bullet”shaped.

The blending percent also depends upon the shape of the final feltedproduct as well as the means by which it is felted or the fibers areotherwise combined prior to needle felting or felting with water. Forexample, when the fibers are organized such as through knitting,crocheting, braiding, knotting, weaving and/or spinning into multipleplies, the conductive properties are reduced, thereby requiring a higherpercentage of conductive fiber in the felting mix. When using a mixtureof 50% conductive fibers and 50% base fibers (by weight), one can knitan I-cord (a spiral knit tube also called idiot cord) to make a tip withthe necessary conductive properties. By knitting the I-cord beforeneedle felting or wet felting, the fibers are pre-tangled beforefelting, resulting in a tip that holds its shape over use with time.When a tip is cut from either end of a felted I-cord, the tip has abullet shape with a rounded end that is finished and will not splay,unravel, or wear as quickly with use as a tip that is made from a cutend of yarn that has been needle felted and wet felted.

In other embodiments, wool roving is spun into a single ply of yarn,which is needle felted by poking repeatedly with barbed felting needleson top of a foam base. Then, the needle felting yarn is wet felted byrolling the yarn back and forth under hot tap water utilizing Dr.Bronner's soap as lubricant. The yarn is then left to air dry and cutinto 11 mm segments. One end of each segment is further cut to achieve arounded, hemispherical tip. The tips are drilled 0.25 inches throughtheir length, and the brass rod is inserted into the resulting hole andaffixed utilizing standard epoxy.

In a class of embodiments, the invention is a stylus for providing inputto a capacitive touch screen, said stylus comprising:

a shaft; and

at least one felted tip supported by the shaft, wherein each said feltedtip is electrically conductive and deformable, and includes base fibersand conductive fibers felted with the base fibers.

Typically, the felted tip is semi-rigid (in the sense that it retainsits shape unless and until it is deformed by forcing it against a touchscreen or other object), has been produced by a process including afelting step, and the base fibers are structured such that the feltingstep results in felted material having interlocking bonds and/or tanglesbetween the base fibers and the conductive fibers that provide thesemi-rigidity. Typically, the felted tip is sufficiently rigid to befunctional as a touch screen stylus tip without any internal structurebeing inserted within it to provide support and/or rigidity, In someembodiments, however, the felted tip comprises a conductive, feltedouter layer, and a conductive supporting structure within the outerlayer. In typical embodiments, the tip is mounted to a conductive postor wire (or other conductive structure) such that the tip and conductivestructure are translatable together as a unit relative to the rest ofthe stylus. Such conductive structure may extend into the tip. The sizeand shape of the felted tip (sometimes referred to as a “contact” tip)are such that the felted tip at an end of a stylus can contact the touchscreen (in an undeformed state and/or a deformed state resulting fromdeformation in response to being forced against the screen) at acoupling area sufficient to stimulate the touch screen (e.g., detectioncircuitry in the touch screen) to recognize a distinct touch by thestylus.

In some embodiments, the undeformed contact tip may be hemispherical(i.e., its distal surface which contacts a touch screen, when it ismounted in a stylus) or spherical. In other embodiments, its distalsurface (which contacts a touch screen) is a truncated cone, or athree-dimensional parabloid, cylindrical or bullet-like.

In some embodiments, the shaft provides a low impedance path capable ofcoupling the capacitance, of the hand (or body) of a user who grips thestylus, via the felted tip, to a touch screen (when the felted tip is incontact with the touch screen). In other embodiments, the stylusincludes at least one switch between the felted tip and the shaft. Whenthe switch is closed the stylus provides a low impedance path capable ofcoupling the capacitance, of the hand (or body) of a user who grips thestylus, via the felted tip, to a touch screen (when the felted tip is incontact with the touch screen). When the switch is open, the stylus doesnot couple the capacitance of the hand (or body) of a user who grips thestylus via the felted tip to a touch screen and the touch screen thuscannot register (recognize) a touch of the felted tip on the touchscreen.

In other embodiments, the stylus includes switched circuitry (includingat least one switch coupled directly or indirectly to an internalcapacitance) between the felted tip and the shaft. When the switch isclosed the stylus provides a low impedance path capable of coupling thecapacitance to a touch screen (when the felted tip is in contact withthe touch screen). When the switch is open, the stylus does not couplethe capacitance via the felted tip to a touch screen and the touchscreen thus cannot register (recognize) a touch of the felted tip on thetouch screen.

In other embodiments, the stylus includes switched circuitry (includingat least one switch) and a capacitance (e.g., the capacitance of a cableor the combined capacitance in conjunction with another object coupledto the stylus) is coupled to the switched circuitry. When the switch isclosed, the stylus provides a low impedance path capable of coupling thecapacitance to a touch screen (when the felted tip is in contact withthe touch screen). When the switch is open, the stylus does not couplethe capacitance via the felted tip to a touch screen and the touchscreen thus cannot register (recognize) a touch of the felted tip on thetouch screen.

In a second class of embodiments, the invention is a capacitive touchstylus having at least a first mode of operation and a second mode ofoperation, and including at least one conductive tip (each, preferably,a conductive felted tip) and switched circuitry (preferably, passiveswitched circuitry) including at least one switch biased in a defaultstate indicative of the first mode of operation but switchable into asecond state indicative of the second mode of operation in response tomovement of the tip (typically, movement of the tip in response toexertion of not less than a threshold force on the tip, e.g., by a touchscreen in response to user-exerted pushing force on the stylus againstthe screen), where the switch is coupled to the tip in one of thedefault state and the second state. The switched circuitry preferablyalso includes a stylus audio port set, including at least one audio portconfigured to be coupled to an audio cable. In typical embodiments inthe second class, the stylus audio port set includes at least one audioinput port, and at least one audio output port, and optionally also aground port. Preferably, the stylus audio port set is configured to becoupled to an end of a conventional audio cable including left and rightoutput channel connectors, a microphone channel connector, and a groundconnector, so that another end of the cable can be coupled to an audioport set (referred to herein as a “host audio port set”) of a touchscreen device, where the touch screen device includes an audio subsystemincluding the host audio port set, and the host audio port set typicallyincludes least two audio output ports (configured to assert left andright output audio channels), an audio output port (configured toreceive an audio input from a microphone), and a ground port.

Typically, the first mode of operation is use of the stylus with its tipin contact with a capacitive touch screen (or other object) with notless than a threshold force being exerted by the object on the tip, andthe second mode of operation is other use of the stylus (e.g., use withthe tip in contact with an object with less than the threshold forceexerted by the object on the tip). In other typical embodiments, thefirst mode of operation is use of the stylus with its tip in contactwith a capacitive touch screen (or other object) with not less than athreshold force being exerted by the object on the tip and the stylusgripped by a user (such that not less than a threshold capacitance iscoupled from the user to the tip), and the second mode of operation isother use of the stylus (e.g., use with the tip in contact with anobject with less than the threshold force exerted by the object on thetip, or with less than the threshold capacitance coupled from to thetip).

In other typical embodiments, the first mode of operation is use of thestylus with occurrence of two events within a predetermined time windowof each other: a threshold capacitance is coupled to the tip (e.g., acapacitance internal to the stylus, or external to the stylus butcoupled to the stylus by the switched circuitry) in response to exertionof not less than a threshold force on the tip (e.g., by a capacitivetouch screen or other object in contact with the tip, as the tip isforced against the object); and a signal is asserted (e.g., fortransmission via an audio cable or other wired link, or a wireless link,to a touch screen device) other than by coupling a capacitance to thetip, but in response to exertion of force on the tip (e.g., by acapacitive touch screen or other object in contact with the tip). Inthese embodiments, the second mode of operation is other use of thestylus (e.g., use with occurrence of one but not both of these events,or with both of the events occurring but not within a predetermined timewindow). The predetermined time window is typically sufficiently wide toallow processing circuitry in a host (touch screen) device to recognizeand distinguish between the two events, but sufficiently short so thatboth events occur in response to a single touch of the stylus on acapacitive touch screen by a user who intends to indicate information tothe touch screen device. In some cases, the first mode is indicated bytwo switches (of the switched circuitry) changing state within thepredetermined window. In some other cases, the first mode is indicatedby one switch (of the switched circuitry) changing state twice withinthe predetermined window.

In some embodiments in the second class, the stylus has a conductive tip(e.g., a conductive, felted tip) that is continuously coupled to asufficient capacitance (when a human user grips the stylus or through astylus body of sufficient capacitance) to allow a capacitive touchscreen device to recognize (as a touch) simple contact of the tip on thescreen of the touch screen device, and the switched circuitry has afirst state which allows the stylus to assert to the touch screen device(e.g., forward to, or loop back from, the touch screen device) a signal(when the stylus is coupled by an audio cable or other link to the touchscreen device) that indicates to the touch screen device that the screen(or another object) is exerting at least a threshold force on the stylustip. The switched circuitry also has a second state which prevents thestylus from asserting such signal to the touch screen device, therebyindicating to the touch screen device that the screen (or other object)is not exerting force (or is exerting less than the threshold force) onthe stylus tip.

In some embodiments in the second class, the stylus has a firstconductive tip at one end (e.g., a conductive felted tip), and a secondconductive tip at another end (e.g., another conductive felted tip). Thefirst conductive tip (e.g., at a “writing” end of the stylus) isconfigured to be moved into a position causing the switched circuitry toenter a first state coupling a capacitance to the tip and opening(open-circuiting) a loop between a first input port (e.g., a left audiochannel input port) of the stylus audio port set and at least one outputport of the stylus audio port set, where the capacitance is sufficientto allow a capacitive touch screen device (e.g., a conventionalcapacitive touch screen device) to recognize (as a touch) simple contactof the first conductive tip on the screen of the touch screen device.Preferably, the switched circuitry is implemented so that both theseevents (coupling of the capacitance to the first conductive tip, andopening the loop between the first input port and said at least oneoutput port of the stylus audio port set) occur within a predeterminedtime window. In response to the first conductive tip being in anotherposition, the switched circuitry enters a second state decoupling thecapacitance from said first conductive tip and/or closing the loopbetween the first input port and said at least one output port of thestylus audio port set. The second conductive tip (e.g., at an “erasing”end of the stylus) is configured to be moved into a position causing theswitched circuitry to enter a third state coupling a capacitance to thetip and opening (open-circuiting) a loop between a second input port ofthe stylus audio port set (e.g., a right audio channel input port) andat least one output port of the stylus audio port set, where thecapacitance is sufficient to allow a capacitive touch screen device(e.g., a conventional capacitive touch screen device) to recognize (as atouch) simple contact of the second conductive tip on the screen of thetouch screen device. Preferably, the switched circuitry is implementedso that both these events (coupling of the capacitance to the secondconductive tip, and closing the loop between the second input port andsaid at least one output port of the stylus audio port set) occur withina predetermined time window. In response to the second conductive tipbeing in another position, the switched circuitry enters a fourth statedecoupling the capacitance from the second conductive tip and/or closingthe loop between the second input port and said at least one output portof the stylus audio port set.

In some embodiments, the invention is a system including a stylus (whichbelongs to the second class of embodiments), a touch screen devicehaving an audio subsystem (including a host audio port set of the typementioned above) and a processor coupled to the audio subsystem, and anaudio cable connected between the stylus audio port set of the stylusand the host audio port set of the touch screen device, wherein theprocessor of the touch screen device is configured to recognize anoperating mode of the stylus in response to at least one response signalreceived at the host audio port set in response to assertion of at leastone signal from the audio subsystem via the host audio port set and thecable to the stylus audio port set.

In some embodiments, the state of the stylus audio port set (e.g., inresponse to the state of the host stylus audio port set) is indicativeof one or more of: contact between a tip of the stylus and a touchscreen (or other object); pressure exerted by a touch screen (or otherobject) on a tip of the stylus; state of at least one sensor of theswitched circuitry; and state of at least one switch of the switchedcircuitry. In some such embodiments, the switched circuitry includes atleast one filter coupled and configured to filter at least one signalreceived from a touch screen device (via an audio cable) at the stylusaudio port set, thereby generating a filtered signal, and the switchedcircuitry is configured to assert the filtered signal at the stylusaudio port set (for transmission to the touch screen device (via theaudio cable).

Typical embodiments in the second class provide a means forcommunicating mode information from a stylus to a host that allows thehost to distinguish between intended touches of the stylus (on acapacitive touch screen) and other touches not intended to be strokes orother kinds of drawing/writing information (such as erasures). Ratherthan to assert mode information actively from a locally powered (active)stylus (including powered sensors and/or switches for determining andasserting the mode information) via wireless communication to or directstimulation of the host, preferred embodiments of the invention usepurely passive switched circuitry in a stylus to assert mode informationto a host via a conventional audio port set conventionally present inthe host and a cable coupled between the stylus and the host. Thesepreferred stylus embodiments do not pulse or otherwise communicate anyinformation through a stylus tip by means of electrical stimulation ofthe host device's touch sensing circuitry other than simple contact(which is recognizable in a conventional manner by a conventional touchscreen device).

In a third class of embodiments of the stylus, the stylus has aconductive tip (e.g., a conductive, felted tip) and includes switchedcircuitry (preferably, passive switched circuitry) having a first statewhich couples a capacitance to the tip, where the capacitance issufficient to allow a capacitive touch screen device (e.g., aconventional capacitive touch screen device) to recognize (as a touch)simple contact of the tip on the screen of the touch screen device, anda second state which decouples the capacitance from the tip, therebypreventing the touch screen device from recognizing (as a touch) simplecontact of the tip on the screen. The capacitance can be a capacitiveload external to the stylus (e.g., the capacitive load of a user's bodywhich can be coupled to the switched circuitry by a conductive shaft ofthe stylus, or another capacitive load which can be coupled to theswitched circuitry) or internal to the stylus (e.g., it can be acapacitor of the switched circuitry). Typically, the switched circuitry(e.g., passive switched circuitry) includes at least one switch biasedin a default state which couples the capacitance to (or decouples thecapacitance from) the tip but is switchable into a second state whichdecouples the capacitance from (or couples the capacitance to) the tipin response to movement of the tip (typically, movement of the tip inresponse to exertion of not less than a threshold force on the tip,e.g., by a touch screen in response to user-exerted pushing force on thestylus against the screen), where the switch is coupled to the tip inone of the default state and the second state. The switched circuitryalso includes a stylus audio port set, including at least one audio portconfigured to be coupled to an audio cable. In typical embodiments inthe third class, the stylus audio port set includes at least one audioinput port, and at least one audio output port, and optionally also aground port. Preferably, the stylus audio port set is configured to becoupled to an end of a conventional audio cable including left and rightoutput channel connectors, a microphone channel connector, and a groundconnector, so that another end of the cable can be coupled to an audioport set (referred to herein as a “host audio port set”) of a touchscreen device, where the touch screen device includes an audio subsystemincluding the host audio port set, and the host audio port set typicallyincludes least two audio output ports (configured to assert left andright output audio channels), an audio output port (configured toreceive an audio input from a microphone), and a ground port.

The switched circuitry of some embodiments of the stylus has a state(e.g., determined by at least one switch actuatable by force of contactof the stylus tip with any surface, e.g., a touch screen) in which itcouples an internal capacitive load (internal to the stylus) to thestylus tip. The switched circuitry of other embodiments of the stylushas a state (e.g., determined by at least one switch actuatable by forceof contact of the stylus tip with any surface) in which it couples tothe tip an external capacitive load (e.g., connects the tip to aconductive shaft of the stylus and thereby to the capacitance of auser's hand gripping the shaft, or couples to the tip anothercapacitance external to the stylus). In some embodiments, the switchedcircuitry includes another switch or sensor actuatable by a first tip ofthe stylus to close or open a circuit path between a first audio outputchannel (of an audio cable coupled between the stylus and a host) and amicrophone input channel (of the cable) to allow routing of a signal(from the host) back to the host either at full strength or attenuatedin proportion the contact force on the first tip. In some embodiments, asecond tip at the opposite end of the stylus has similar properties, andthe switched circuitry also includes switch or sensor actuatable by thesecond tip to close or open a circuit path between a second audio outputchannel (of an audio cable coupled between the stylus and a host) and amicrophone input channel (of the cable) to allow routing of a signal(from the host) back to the host either at full strength or attenuatedin response (e.g., proportionally) to the contact force on the secondtip.

Audio signals generated by a host (e.g., comprising frequency componentsof multiple frequencies that are mixed together, or pulse trains) can beasserted via an audio cable to the stylus. These signals can be returned(looped back, with optional attenuation) to the host, or not returned tothe host, depending on the state of passive switched circuitry in thestylus. For example, signals asserted to the stylus on left and rightaudio channels could have different frequency content (e.g., one couldcomprise frequency components in a first band; the other comprisingfrequency components in a different band) for easier discriminationprocessing (by the host) of signals returned to the host from thestylus.

The switched circuitry of the stylus can include one or more switches,or at least one switch and at least one variable circuit element (e.g.,a sensor or source) whose state is determined by sensor input (e.g.,force, slider position, or position of a rotatable annular ring). Eachswitch of the switched circuitry has a subset of the functions of onetype of variable sensor, in the sense that the switch has either of twostates (0 or 100%), whereas the sensor can be indicative of more thantwo states (e.g., a continuous range of levels). One type of sensor ofthe switched circuitry is (or includes or is coupled to) a filterconfigured to filter a signal (e.g., an audio signal) from a host, sothat when the filtered signal is returned to the host (e.g., via themicrophone input channel of an audio cable between the stylus and host)the host can process the filtered signal to determine the output of therelevant sensor (and/or to identify which of several sensors in thestylus the signal is indicative of).

In some embodiments, the switched circuitry of the stylus presents acapacitive load (i.e., couples the load through a closed switch andconductive material of the stylus body from a user's hand which gripsthe body, or from a capacitor within or external to the stylus. In thelatter case, the stylus body can be insulating) to the stylus tip (incontact with a touch screen) and thereby to conventional touch screensensors to cause the touch screen to sense a “touch” event (“Event 1”).The switch which presents this load to the stylus tip may be biased tobe open when less than a threshold force is exerted on the tip (e.g., bya capacitive touch screen in contact with the tip). However, this initself does not disambiguate between a stylus tip touch and a finger (orhand) or other non-stylus touch. Thus, the switched circuitry caninclude at least one other switch which, when closed (by “Event 2”),closes a loop between the stylus and the host touch screen device, saidloop including an audio output channel (of a cable connected between thestylus and the host), circuit elements in the stylus, and anotherchannel (e.g., a microphone input channel) of the cable. In response toEvent 2, circuitry in the touch screen device (e.g., audio circuitrywhich is normally used to process microphone input signals) also sensesa “tip” event (and optionally also receives and recognizes the output ofone or more sensors and/or switches within the stylus). Circuitry in thetouch screen device interprets, as a stylus touch, the occurrence of“Event 1” within a predetermined time window (“x” seconds) of “Event 2.”Circuitry in the touch screen device interprets, as a non-stylus touch,the occurrence of an “Event 1” that is not followed within x seconds (ornot preceded by x seconds, in some embodiments) by an “Event 2.” Theduration of the window “x seconds” is preferably predetermined in amanner that depends on expected processing delays (e.g., the delayinherent in any required Fourier transform and/or other processing ofthe signals sensed by the touch screen device including its screencircuitry and its audio circuitry).

In various embodiments, the inventive stylus is a powered, non-powered,active, or passive device. For example, it is contemplated that someembodiments of the stylus is specially designed to draw power (e.g.,about half a Watt) from an audio output channel (and/or other channels)of a cable connected between the stylus and a host, for use by op ampsor other circuit elements in the stylus. In operation, other embodimentsof the stylus would not draw power from a host (or would draw no morethan an insignificant amount of power from a host, e.g., no more thanvery small amounts of power unavoidably dissipated as heat due toresistance of circuit elements in the stylus).

In some embodiments, the invention is a stylus for a capacitive touchscreen which is configured to mechanically stimulate the touch screenand to assert modal information to the touch screen by patterneddisconnection of a capacitive load (either external to the stylus, e.g.,provided by the body of a human gripping the stylus, or internal to thestylus) via purely mechanical means of winding or shaking. For example,the stylus is capable of being powered (e.g., re-charged) in response toa shaking, twisting, or general user motion by means of an internalmechanism that translates the mechanical energy into electrical energy(e.g., for recharging a battery local to the stylus, or for use directlyby the stylus for its operation). The touch screen is configured toimplement a method for recognizing such a stimulus pattern to select amodality of interaction with the stylus.

In some embodiments, the invention is a stylus which is configured tostimulate a capacitive touch screen mechanically and to communicatemodal information to the touch screen (e.g., by patterned disconnectionof circuitry within the stylus) via a wireless link (e.g., an RF link),where power consumed by the stylus during operation is derived frommechanical means local to the stylus (e.g., within the stylus), e.g., byshaking or twisting the body of the stylus. The touch screen isconfigured to implement a method for recognizing such a stimulus patternto select a modality of interaction with the stylus.

In some embodiments, the invention is a stylus which is configured tostimulate a capacitive touch screen mechanically and to communicate (tothe touch screen) stylus identification data that uniquely identifiesthe stylus (or a user thereof). The touch screen device is configured(e.g., includes a processor programmed with application software) toidentify the stylus (or user) in response to the stylus identificationdata, e.g., so that the touch screen device can operate in differentmodes in response to input from each of multiple styli. For example, thetouch screen device implements an annotation application that uses aunique identification of each stylus to identify a unique user and tocapture and/or display the user's name and or other specific informationthat is tied to that user.

In some embodiments, the tip actuation signals from the stylus to thehost device may be provided to the host device through, for example, theDOCK connector on a host device that provide power to the stylus fromthe host device (the DOCK connector is a docking connector that hasmultiple signals in it: audio, USB, RS232, etc). The tip actuationsignals may also be provided through a USB connection (that is also mayprovide power to the stylus from the host device) through a USB cable.The tip actuation signal may be provided to the host device utilizingany data communications protocol (e.g., RS232, WiFi, BlueTooth, CAN,etc.); if it is a wireless protocol, then a stand-alone power source(e.g., battery) is needed. An aspect of the tip-to-touch disambiguationalgorithm relies on a data communications means, either parallel orserial, that is capable of representing and transmitting the followingevents in at least one direction (from the stylus to the host device) ina timely manner:

TIP(n) depressed (sufficient actuation force applied)

TIP (n) released (insufficient actuation force applied)

wherein n represents the tip number.

In an embodiment, a system is provided having a capacitive touch screendevice comprising a capacitive touch screen surface; and a controllerthat defines a touch screen event on the capacitive touch screen surfaceby the touch event having at least a threshold contact area value and atleast a threshold change in local capacitance value; and a styluscomprising a tip with a conductive surface coupled to a capacitance, thetip of capacitance switchable from a first state (tip down) in which thetip coupled to the capacitance stimulates the capacitive touch screensurface to a second state (tip up) in which the tip does not stimulatethe capacitive touch screen surface. This system is used to perform amethod comprising (a) transmitting from the stylus to the capacitivetouch screen device a signal associated with a transition in the stylusfrom the tip up state to the tip down state and assigning a time T1 tothat signal; (b) on the capacitive touch screen device, gathering alltouch event data, including touch events, if any, associated withcontact between the stylus tip in the tip down state and the capacitivetouch screen; (c) for gathered touch events that occurred within apredetermined time interval relative to T1, creating a collection ofunclassified touch event data; and (d) processing the collectedunclassified touch event data to differentiate touch events likelycaused by movement of the stylus tip in the tip down state from touchevents likely caused by touches of the capacitive touch screen objectsother than the stylus.

In some embodiments, the invention is a capacitive touch screen devicethat is configured to recognize (e.g., includes a processor programmedto recognize) an operating mode of an embodiment of the inventive stylusin response to at least one signal indicative of the state of switchingcircuitry in the stylus, and in response to touch screen sensor data(i.e., data generated and processed conventionally in touch screendevices to calculate a centroid from an outline of an object's contactarea on a touch screen) including by processing the touch screen sensordata in at least one of the following additional ways beyond the timewindow method ways: disambiguating movement of the stylus on the screenversus non-stylus strokes by predicting a future location of contactarea of the stylus on the screen (e.g., by determining a vectorestablished by the previous sequence of centroids (or other measures ofthe location) of each previous user strokes of the moving stylusassigned contact areas on the touch screen and establishing aprobability that the tip generated stroke will be coincident with thatvector by using a process of dead reckoning); determining velocity ofeach segment within the contact stroke on the screen and using athreshold to eliminate all strokes that contain segments that exceed acertain threshold velocity; determining acceleration of each segmentwithin the contact stroke on the screen and establishing a probabilitythat the stroke is intended or spurious using mathematical functions ofacceleration; determining the acceleration between the end of thepreviously classified tip stroke and the beginning of the current strokeand establishing a probability that the stroke is intended or spurioususing mathematical functions of acceleration; determining a measure ofthe location of currently active “palm” strokes classified by previousprocessing (e.g., by assuming all non-tip strokes must be palm strokes)and using the relative locations of these active palm strokes to createa probability that the unclassified stroke is intended or spurious usinga mathematical function of the distance between said palm locations andthe unclassified stroke. In the absence of prior information (i.e.,first touch, or a touch that occurs after a certain time threshold, andno currently active palm location), the method establishes a probabilitythat each stroke is generated by a stylus or palm based on a function(e.g., median, mean or median absolute deviation from the median) of thelength of segments in the stroke. These techniques alone or incombination can allow (or help to allow) the touch screen device todisambiguate between user-intended stylus touches on the screen andnon-intended or spurious “palm” touches.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of the stylus in use witha capacitive touch screen device.

FIG. 2 is a side cross-sectional view of stylus 1 of FIG. 1, showingfelted tip 11 of the stylus mounted on post 9 which extends through tipholder 7 at the distal end of shaft 5 of the stylus.

FIG. 3 is a perspective view of conductive, felted stylus tips 11, 21,and 22, each useful as an element of an embodiment of the stylus andeach having a different shape. Each of tips 11, 21, and 22 is formedwith a hole (a respective one of holes 11A, 21A, and 22A, as shown)extending partially through the tip for receiving the distal end of post9.

FIG. 4 is a perspective view of a detail of metal supporting rod 9 (ofFIG. 2) with hooks 10 for retention of felted tip 11.

FIG. 5 is a perspective view of a spherical conductive felted stylus tipwith a spherical shape, and a side cross-sectional view of the stylustip mounted in direct contact with the shaft of an embodiment of thestylus. The tip is held to the shaft by friction or by an adhesive.

FIG. 6 is a perspective view of another conductive felted stylus tip ofa hemispherical shape, and a side cross-sectional view of the stylus tipmounted in direct contact with the shaft of an embodiment of the stylus.The tip is held to the shaft by friction or by an adhesive.

FIG. 7 is a perspective view of another conductive felted stylus tip ofa bullet shape, and a side cross-sectional view of the stylus tipmounted in direct contact with the shaft of an embodiment of the stylus.The tip is held to the shaft by friction or by an adhesive.

FIG. 8 is a perspective view of an embodiment of the stylus (havingconductive stylus tips at both ends) in use with a capacitive touchscreen device.

FIG. 9 is a simplified side cross-sectional view of an embodiment of thestylus having conductive stylus tips at both ends of its shaft 46, witha circuit diagram of passive switched circuitry within shaft 46. Stylus45 of FIG. 9 is coupled by a conventional audio cable 49 to capacitivetouch screen device 40 (which includes touch screen 42 and processor41).

FIG. 10 is a block diagram of elements of an embodiment of the stylus,coupled with elements of a capacitive touch screen device.

FIG. 11 is a flow chart of steps performed in operation of an embodimentof the stylus and a capacitive touch screen device.

FIG. 12 is another flow chart of steps performed in operation of anembodiment of the stylus and a capacitive touch screen device.

FIG. 13 is a state diagram for a finite state machine diagram forclassifying strokes into FINGER, TIP, or PALM strokes representative ofan embodiment of the stylus and a capacitive touch screen.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the stylus that include a felted tip will be describedwith reference to FIGS. 1-7. Other embodiments of the stylus thatinclude at least one felted tip and switched circuitry, and systemsincluding a touch screen device and such an embodiment of the stylus,will be described with reference to FIGS. 8-12.

In a first class of embodiments, a stylus is provided for input to acapacitive touch screen. The stylus has a tip comprising (e.g.,consisting of) conductive felt (e.g., felted tip 11 of FIG. 1, or feltedtip 21 or 22 of FIG. 3) which provides a deformable conductive surfacefor contacting a touch screen (with a sufficiently large contact area toallow the touch screen to recognize a touch by the tip), and is capableof being moved in contact with the touch screen with less than anundesirable amount of friction (between the tip and a touch screensurface in contact therewith). The tip comprises first fibers (which aresometime referred to herein as “base” fibers, and are typicallynon-conductive) and conductive fibers, and is produced by felting thebase fibers with the conductive fibers using the fiber materialtechnique commonly known as felting. For example, felted tip 11 of FIG.1 (better shown in FIG. 3) has base fibers B felted with conductivefibers C. The base fibers are selected to be conducive to felting (i.e.,to have properties at the microscopic level that allow them to bond andtangle with one another in the presence of water), to have sufficientsoftness, flexibility, non-abrasiveness and low friction to producesufficiently low friction when used (after being felted) as a capacitivetouch screen stylus tip, and preferably to have low cost. During thefelting process, the base fibers capture the conductive fibers and forma spherical, hemispherical or bullet-like felt object (or a felt objectof other shape) that is semi-rigid (in the sense in the sense that itretains its shape unless and until it is deformed by forcing it againsta touch screen or other object), and can be mounted to a distal end of asupport to form a stylus. In use of the stylus, the felt objectfunctions as a stylus tip that couples a sufficient capacitance to atouch screen, at a contact region on the screen of sufficient area, toallow recognition of a touch by the tip. In an embodiment, the tip byitself does not have sufficient capacitance to allow recognition of atouch by the tip.

As shown in FIG. 1, stylus 1 is an embodiment of the stylus whichincludes felted tip with a conductive surface 11. Tip 11 is in contactwith screen 3A of capacitive touch screen device 3. As best shown inFIG. 2, felted tip 11 is mounted on conductive post 9 which extendsthrough tip holder 7 at the distal end of shaft 5 of stylus 1. Post 9has hooks 10 (best shown in FIG. 4) for retaining the tip to the rest ofthe stylus, and is a conductive member (e.g., a metal rod or tube) thatprotrudes distally from tip holder 7. Shaft 5 is conductive and hollow,and short conductive wire 13 connects post 9 to conductive shaft 5.Alternatively, hooked supporting rod 9 is replaced by a hookless metalrod with adhesive material at its distal end to hold felted tip 11 (oranother embodiment of the felt tip) in place at an end of the stylus.

In variations on the FIG. 2 embodiment, post 9 is not coupled at alltimes to shaft 5. Instead, post 9 is configured to engage a switch(e.g., switch S1 of FIG. 9) of switched circuitry in the stylus, saidswitch being coupled to shaft 5 (or to a capacitance internal orexternal to the stylus), and post 9 is spring-biased to keep the switchin a normally open state, and is movable (in response to felted tip 11being pressed against a touch screen or other object) to close theswitch to couple felted tip 11 to shaft 5 (or to the internal orexternal capacitance). In the latter case, post 9 can be considered tobe an element of the switch, so that the switch is coupled to tip 11 andis either open or closed depending on whether at least a threshold forceis exerted (e.g., by screen 3A of touch screen device 3) on tip 11.

In some embodiments, the undeformed shape of a conductive, felted tip ofthe stylus is hemispherical (i.e., its distal surface which contacts atouch screen, when it is mounted in a stylus, is hemispherical),spherical or bullet-like. In other embodiments, its distal surface(which contacts a touch screen) is a truncated cone or athree-dimensional parabloid.

FIG. 3 is a perspective view of felted stylus tips 11, 21, and 22, eachuseful as an element of an embodiment of the stylus and each having adifferent shape. The distal surface of tip 21 is hemispherical, and thedistal surface of tip 22 is a three-dimensional paraboloid. Felted tip11 is shown to comprise base fibers B felted with conductive fibers C.Each of tips 11, 21, and 22 is formed with a hole (a respective one ofholes 11A, 21A, and 22A, as shown) extending partially through the tipfor receiving the distal end of post 9. Alternatively, each of the tipsis not preformed with such a hole, and the post is simply pushed intothe tip during assembly of the apparatus.

FIG. 5 is a perspective view of a spherical, conductive, felted stylustip 11A, and a side cross-sectional view of tip 11A mounted in directcontact with a distal end of shaft 5 of an embodiment of the stylus. Tip11A is held to shaft 5 by friction or by an adhesive.

FIG. 6 is a perspective view of another conductive felted stylus tip(21A) and a side cross-sectional view of tip 21A mounted in directcontact with a distal end of shaft 5 of an embodiment of the stylus. Tip21A's cylindrical proximal end 21C is held to shaft 5 by friction, ortip 21A is held to shaft 5 by an adhesive. The distal surface of tip 21Ais a three-dimensional parabloid.

FIG. 7 is a perspective view of another conductive felted stylus tip(21B) and a side cross-sectional view of tip 21B mounted in directcontact with a distal end of shaft 5 of an embodiment of the stylus. Tip21B's cylindrical proximal end 21D is held to shaft 5 by friction, ortip 21B is held to shaft 5 by an adhesive. The distal surface of tip 21Bis hemispherical.

The technique for manufacturing typical embodiments of the stylus tipstarts with a base fiber (preferably a common, inexpensive base fiber)that is already conducive to felting. Wool or any other fiber that hasscales which interlock at the microscopic level during a felting processis suitable as a base fiber in many embodiments. Interspersing this basefibers with conductive fibers, which typically do not have the samemicroscopic characteristics necessary for felting, allows the basefibers to lock and hold the strands of the conductive fibers. Thefelting should produce a semi-rigid, felt object having shape suitablefor use as the tip of a capacitive touch screen stylus (e.g., spherical,hemispherical or bullet-like shape), and size suitable for affixing tothe end of a capacitive touch screen stylus body (e.g., a conductive rodor tube, or a non-conductive tube including or coupled to a capacitance,where the capacitance is connected by a conductor to the felt object inat least one operating mode). When the stylus has a conductive body, theconductive body (and optionally a conductive structure between the felttip and the conductive body) couples with the human hand and thereforeprovides a low impedance path between the conductive felted tip and thehuman body, allowing a capacitive touch screen to properly calculate acentroid based on the area of contact between the tip and the screen. Byusing base fibers of sufficiently low friction (when felted) in the tip,the coefficient of friction of the felted tip against the glass surfaceof a capacitive touch screen is significantly low to allow for a natural(pen-like) feel of the stylus as the tip slides on (or is touchedagainst) the screen.

The blending percentage of the conductive fibers and diameter of thefelted tip can be chosen to be optimal for the intended use of thecapacitive touch screen stylus. The minimum capacitive load to becoupled via the tip, and the minimum two-dimensional contact area of thetip with the screen, will depend on the host device with which thestylus is used. The conductive fibers can be any fibers that inherently(or are modified to) have electrical resistivity preferably less than10,000 ohms-cm (and not more than on the order of 10,000,000 ohms-cm).To produce the tip, the base and conductive fibers are mixed in a ratiosufficient for the tip to have sufficient conductivity to provide theelectrical coupling necessary for a stylus including the tip tostimulate a capacitive touch screen. The tip's conductive fibers (ratherthan any other element of the tip) provide the tip's conductivity thatis required for its intended use (e.g., the conductive tip is normallyused when dry, but even if it happens to be used when wet with aconductive liquid or contaminated with a conductive substance, it doesnot rely on the liquid's or the contaminant's conductivity to be usefulas a capacitive touch screen stylus tip).

Examples of conductive fibers suitable in typical embodiments includebut are not limited to carbon fibers, fibers coated with metal, andfibers coated with carbon. The exemplary conductive fibers havelow-friction and non-abrasiveness properties similar to those of typicalbase fibers with which they are felted. Thus, when felted with the basefibers to produce a stylus tip, the tip can have acceptably low frictionand non-abrasiveness. In contrast, metal wires are typically moreabrasive than the exemplary conductive fibers. Thus, a tip consisting(or including a significant quantity) of metal wires would typicallyabrade the surface of a touch screen during use.

In some embodiments, the tip comprises 1/3 conductive fibers and 2/3base fibers. The conductive fibers may comprise Jarden MaterialsRESISTAT® TYPE F9216, merge L040, nylon electrically conductive withcarbon suffused onto the fiber surface, cut into 4 inch lengths andhaving a resistance of 4000 ohm/cm. The base fibers may comprise 18.5micron Merino wool fibers. In this instance, 0.06 grams total materialfelts into a ball approximately 0.250″ in diameter The weight isapproximately 0.05 grams per piece. A 1/16″ diameter brass rodapproximately 1.85″ long may be utilized as support structure for thetip. The tip may be constructed by mixing the wool base fiber with theconductive fiber using a drum carder to achieve uniform mixing. Thematerial is weighed and separated into 0.06 gram amounts. Balls are spunin a toroidal shaped grooved mold with a standard hand drill @ 1000 RPMunder hot tap water utilizing Dr. Bronner's soap as a lubricant. Theballs are then left to air dry. The air dried balls are then drilled 50%through and the brass rod is inserted into the resulting hole andaffixed utilizing standard 5 minute epoxy.

In some embodiments, the above-mentioned conductive and base fibers aremixed according to the 1/3 conductive fiber, 2/3 wool fiber ratio. Themixture strands are then felted into a cord by water and soap and handrolling and stretching the cord to achieve a uniform cylinder with acircular cross-section. The cylindrical diameter may be ⅛″. The strandsare then cut into desired lengths, e.g. 0.25″. The brass rod is theninserted into the center of one circular face of the cylinder andepoxied into place utilizing, for example, standard 5 minute epoxy. Theother circular face of the cylinder may then be trimmed to provide ahemispherical end to the cylinder to make the tip structure “bullet”shaped.

The blending percent also depends upon the shape of the final feltedproduct as well as the means by which it is felted or the fibers areotherwise combined prior to needle felting or wet felting with water.For example, when the fibers are organized such as through knitting,crocheting, braiding, knotting, weaving and/or spinning into multiplyplies, the conductive properties are reduced, thereby requiring a higherpercentage of conductive fiber in the felting mix. When using a mixtureof 50% conductive fibers and 50% base fibers (by weight), one can knitan I-cord (a spiral knit tube also called idiot cord) to make a tip withthe necessary conductive properties. By knitting the I-cord beforeneedle felting or wet felting, the fibers are pre-tangled beforefelting, resulting in a tip that holds its shape over use with time.When a tip is cut from either end of a felted I-cord, the tip has abullet shape with a rounded end that is finished and will not splay,unravel, or wear as quickly with use as a tip that is made from a cutend of yarn that has been needle felted and wet felted.

In other embodiments, wool roving is spun into a single ply of yarn,which is needle felted by poking repeatedly with barbed felting needleson top of a foam base. Then, the needle felting yarn is wet felted byrolling the yarn back and forth under hot tap water utilizing Dr.Bronner's soap as lubricant. The yarn is then left to air dry and cutinto 11 mm segments. One end of each segment is further cut to achieve arounded, hemispherical tip. The tips are drilled 0.25 inches throughtheir length, and the brass rod is inserted into the resulting hole andaffixed utilizing standard epoxy.

In a class of embodiments, the invention is a stylus for providing inputto a capacitive touch screen, said stylus comprising:

a shaft (e.g., conductive shaft 5 of FIG. 2, or non-conductive shaft 46of FIG. 9 to be described below); and

at least one felted tip (e.g., tip 11 of FIG. 2, or tips T1 and T2 ofFIG. 9) supported by the shaft, wherein each said felted tip iselectrically conductive and deformable, and includes base fibers andconductive fibers felted with the base fibers.

Typically, the felted tip is semi-rigid (in the sense that it retainsits shape unless and until it is deformed by forcing it against a touchscreen or other object), has been produced by a process including afelting step, and the base fibers are structured such that the feltingstep results in felted material having interlocking bonds and/or tanglesbetween the base fibers and the conductive fibers that provide thesemi-rigidity. Typically, the felted tip is sufficiently rigid to befunctional as a touch screen stylus tip without any internal structurebeing inserted within it to provide support and/or rigidity The fibersare randomly distributed throughout the felt with regions of higherdensity and other regions of lower density of conductive fibers. Theblending is sufficient so that the density of the conductive fibersthroughout the tip is sufficient to allow for the required conductivity,and the wool is distributed sufficiently to hold the conductive fiberstogether after felting.

In some embodiments, however, the felted tip comprises a conductive,felted outer layer, and a conductive supporting structure within theouter layer. In typical embodiments, the tip is mounted to a conductivepost or wire (or other conductive structure) such that the tip andconductive structure are translatable together as a unit relative to therest of the stylus. Such conductive structure may extend into the tip.The size and shape of the felted tip (sometimes referred to as a“contact” tip) are such that the felted tip at an end of a stylus cancontact the touch screen (in an undeformed state and/or a deformed stateresulting from deformation in response to being forced against thescreen) at a coupling area sufficient to stimulate the touch screen(e.g., detection circuitry in the touch screen) to recognize a distincttouch by the stylus.

In some embodiments, the shaft (or the shaft and a conductive structurecoupled thereto) provides a low impedance path (e.g., the path throughshaft 5, wire 13, and post 9 of FIG. 2) capable of coupling thecapacitance, of the hand (or body) of a user who grips the stylus, viathe felted tip, to a touch screen (when the felted tip is in contactwith the touch screen). In other embodiments, the stylus includes atleast one switch between the felted tip and the shaft. When the switchis closed the stylus provides a low impedance path capable of couplingthe capacitance, of the hand (or body) of a user who grips the stylus,via the felted tip, to a touch screen (when the felted tip is in contactwith the touch screen). When the switch is open, the stylus does notcouple the capacitance of the hand (or body) of a user who grips thestylus via the felted tip to a touch screen and the touch screen thuscannot register (recognize) a touch of the felted tip on the touchscreen.

In other embodiments, the stylus includes switched circuitry (includingat least one switch coupled directly or indirectly to an internalcapacitance) between the felted tip and the shaft. When the switch isclosed the stylus provides a low impedance path capable of coupling thecapacitance to a touch screen (when the felted tip is in contact withthe touch screen). When the switch is open, the stylus does not couplethe capacitance via the felted tip to a touch screen and the touchscreen thus cannot register (recognize) a touch of the felted tip on thetouch screen.

In other embodiments, the stylus includes switched circuitry (includingat least one switch) and a capacitance (e.g., the capacitance of a cableor the combined capacitance in conjunction with another object coupledto the stylus through the cable) is coupled to the switched circuitry.When the switch (e.g., switch S2 or S4 of FIG. 9) is closed, the stylusprovides a low impedance path (e.g., the path through tip T1 and switchS2 and audio cable 49, or tip T2 and switch S4 and audio cable 49, ofFIG. 9) capable of coupling the capacitance (e.g., the capacitance ofcable 49) to a touch screen when the felted tip is in contact with thetouch screen. When the switch is open, the stylus does not couple thecapacitance via the felted tip to a touch screen and the touch screenthus cannot register (recognize) a touch of the felted tip on the touchscreen.

We next describe a second class of embodiments and a third class ofembodiments of the invention with reference to FIGS. 8, 9, 10, 11, and12.

FIG. 8 shows an embodiment of the stylus (100) that has two conductivetips 102(1) and 102(2) at opposite distal ends of the stylus. Each ofconductive tips 102(1) and 102(2) is preferably a conductive felted tip,and each provides a contact surface for engagement with capacitive touchscreen 105 of host device 104. Stylus 100 also includes switchedcircuitry (not shown) coupled to tips 102(1) and 102(2) and including astylus audio port set (including left and right channel audio outputports, a microphone input port, and a ground port) coupled to one end ofaudio cable 103. The other end of cable 103 is coupled to a conventionalaudio port set (including left and right channel audio output ports, amicrophone input port, and a ground port) of host device 104. Cable 103is a conventional audio cable which includes conductors that implementleft and right audio output channels (conventionally used for drivingleft and right transducers of audio headphones), a microphone inputchannel, and system ground. Host device 104 can be any capacitive touchscreen device having an audio port set (and audio circuitry coupledthereto).

Many conventional devices that include capacitive touch screens are alsocapable of producing one or two output audio signals capable of poweringheadphones (e.g., left and right channels of a stereo audio signalasserted from device 104 via cable 103 to a pair of headphones). Thesesignals are typically intended for the left and right ear transducers ofa pair of headphones, but are asserted to switched circuitry of a touchscreen stylus in accordance with some embodiments of the presentinvention. Many conventional touch screen devices are also typicallyconfigured to receive a microphone input (e.g., a microphone inputsignal asserted from a microphone via cable 103 to device 104). Someembodiments of the stylus utilize these existing signal paths and a setof contact actuated switches and/or sensors with optional filters tosend signals to a host device (e.g., to a processor in a host devicethat runs application software). Typically, the host sends pre-definedsignal patterns over the audio output channels, and processes thesignals received back from the stylus in response (over the microphoneinput channel) to determine a mode of interaction with the stylus (e.g.,including by determining contact and/or force exerted by a touch screenon a first tip (e.g., tip 102(1) of FIG. 8) of the stylus, contactand/or force exerted by a touch screen on a second tip (e.g., tip 102(2)of FIG. 8) of the stylus, no contact by a stylus tip, and other modalinformation that may be encoded via switches or sensors of switchingcircuitry within the stylus).

FIG. 9 is a simplified side cross-sectional view of stylus 45 which isanother embodiment of the stylus, shown coupled by conventional audiocable 49 to a capacitive touch screen device 40. Device 40 includescapacitive touch screen 42 (which can have conventional design) andprocessor 41 connected to receive signals from screen 42 indicative oftouches and/or strokes on screen 42. The body (shaft) 46 of stylus 45 isnon-conductive and hollow. Stylus 45 also includes passive switchedcircuitry mounted to shaft 46, and FIG. 9 includes a circuit diagram ofthe passive switched circuitry.

The passive switched circuitry of stylus 45 includes a stylus port setthat can be (and is, as shown in FIG. 9) coupled to an end of cable 49.The stylus port set includes microphone output port MIC, left channelaudio input port L, right channel audio input port R, and ground portGND. Ports MIC, L, R, and GND are coupled respectively to microphonesignal, left audio channel, right audio channel, and ground conductorsof cable 49. The conductors of cable 49 are enclosed within aninsulator. The GND wire alone, or when connected to the host device, mayprovide sufficient capacitance when coupled to tip T1 (or T2) of stylus45 to allow conventional capacitive touch screen elements of device 40to recognize a touch of tip T1 (OR T2) on screen 42.

Device 40 includes a stylus port set coupled to the other end of cable49, and including microphone input port MIC′, left channel audio outputport L′, right channel audio output port R′, and a ground port GND′.

Stylus 45 includes conductive tip T1 (preferably an embodiment of thefelted tip) mounted on conductive post P1 which extends through (and istranslatable relative to) tip holder H1 at the left end of shaft 46.Spring 51 is compressed between the edge of the printed circuit board,50, and the right end surface of the contact point CP1 which is rigidlyattached and translates with conductive post P1. Holder H1 centers postP1 and tip T1 within shaft 46 with freedom to translate inward (to theright in FIG. 9) toward shaft 46 when pressed against screen 42 ofdevice 40. Contact point CP1 is electrically isolated from conductivepost P1. Contact points CP2 and CP3 show the remaining componentsnecessary for S2 to function as a switch. CP2 and CP3 are rigidlyattached to holder H1 and provide the completion of the circuit when CP1is in simultaneous contact with CP2 and CP3. Tip T1, conductive post P1,holder H1, contact points CP1, CP2, CP3 and spring 51 comprise assemblyA1.

Stylus 45 also includes conductive tip T2 (preferably an embodiment ofthe felted tip) which is shown as part of assembly A2. A2 an identicalassembly to assembly A1 except the translation motion of P2 moves to theleft in FIG. 9 when pressed against screen 42 of device 40.

In typical use, tip T1 is used to “write” on screen 42 by making strokes(recognized by processor 41 as touches on screen 42) which compressspring 51 to move post P1 so as to open a normally closed switch S2(comprised of contact points CP1, CP2, and CP3) and then (within apredetermined time window) close switch S1. In typical use, tip T2 isused to “erase” a mark (that has previously been caused to be displayed)on screen 42 by making strokes (recognized by processor 41 as touches onscreen 42) which compress spring 53 to move post P2 so as to open anormally closed switch S4 and then (within a predetermined time window)close switch S3.

The elements of the passive switched circuitry that are mounted withinshaft 46 include normally closed switch S2 connected to audio input L onone pole of S2 and resistor R1 on the other pole of S2. Resistors R1 andR2 serve as a voltage divider attenuator between S1 and ground. Viewedin isolation from the rest of the circuit (i.e. only considering theinteraction of L, R1, R2, and S2) node N represents either no signal (ifS2 is open) or the attenuated output of the L signal (if S2 is closed).The passive switched circuitry also includes resistors R5, R6, switch S4and audio channel R. These circuits mirror the functions of R1, R2, S2for the Right audio channel combined with the actuation of T2.

In operation of the FIG. 9 system, processor 41 asserts audio signals tostylus 45 via the left and right audio channels of cable 49. The audiosignal asserted from processor 41 to port L′ of host 40 may comprisefrequency components in a first band. The audio signal asserted fromprocessor 41 to port R′ of host 40 may comprise frequency components ina second band (distinct from the first frequency band). The audio signalasserted at port L′ can propagate through cable 49 to port L of stylus45 and either be returned (looped back through the loop includingresistor R1, switch S2, capacitor C1, and the microphone, MIC, channelof cable 49) to host 40, or not returned to the host, depending on thestate of switch S2 in stylus 45. The audio signal asserted at port R′can propagate through cable 49 to port R of stylus 45 and either bereturned (looped back through the loop including resistor R5, switch S4,capacitor C1 and the microphone channel of cable 49) to host 40, or notreturned to the host, depending on the state of switch S4. The differentfrequency content of the signal returned through each loop allowsprocessor 41 to distinguish between an event in which switch S2undergoes a transition between open and closed states, and an event inwhich switch S4 undergoes a transition between open and closed states.

The resistances of resistors R1 and R2 should be selected so that thevoltage across resistor R2 (in operation of stylus 45 with a leftchannel audio signal of typical voltage asserted from device 40 viacable 49 to the loop comprising resistors R1 and R2, capacitor C1, andswitch S2) is suitable (and no more than desirable) for asserting backto cable 49 a return signal of suitable amplitude (in response to theleft channel audio signal) for processing by device 40 to recognizeintended touches on screen 42 by tip T1. Similarly, the resistances ofresistors R5 and R6 should be selected so that the voltage acrossresistor R6 (in operation of stylus 45 with a right channel audio signalof typical voltage asserted from device 40 via cable 49 to the loopcomprising resistors R5 and R6, capacitor C1 and switch S4) is suitable(and no more than desirable) for asserting back to cable 49 a returnsignal of suitable amplitude (in response to the right channel audiosignal) for processing by device 40 to recognize intended touches onscreen 42 by tip T2.

The resistor R3 connected to GND may be required by the host device toinform it that a microphone input is available. In host devices that donot require this specific stimulus, R3 may be omitted. The resistance ofR3 is chosen based on the specifications of the host device and maytherefore vary.

The capacitor C1 is used to achieve the AC coupling of the audio signaland to allow for the proper operation of resistor R3 (if required by thehost device 40). The value of C1 is chosen in relationship to thefrequencies bands that are sent by host 40 to the stylus 45. CapacitorC1 serves as a high pass filter and will attenuate lower frequencies.Node Q indicates the mixing point of the switched and attenuated signalsfrom the L and R channels before AC coupling in capacitor C1.

The passive switched circuitry of stylus 45 also includes normally openswitch S1 between post P1 and the ground port GND, and normally openswitch S3 between post P2 and the ground port GND. Switch S2, whichcomprises the right edge of post P1 and the printed circuit board edgecontact point CP4, is open when post P1 is in its normal state (biasedtoward the left of FIG. 9 by spring 51), and is positioned relative topost P1 so as to enter its closed state when P1 is pushed inward (to theright of FIG. 9) into engagement with CP3 in a mode of operation inwhich tip T1 is pressed against screen 42. Switches S2 and S1 arepositioned relative to each other (and relative to post P1) such thatwhen tip T1 is pressed against screen 42 with sufficient force (and withtypical speed) by a user, contact points CP2 and CP3 translate (withshaft 46) to the left causing contact point CP1 (rigidly attached topost P1) to move out of engagement with CP2 and CP3 (thereby openingswitch S2), and as shaft 46 (with rigid attachment to contact point CP4of switch S1) continues to translate to the left, CP4 engages the edgeof post P1 (within a predetermined time window after the opening ofswitch S2) to close switch S2. The closing of switch S1 couples thecapacitive load presented by cable 49 (through port GND and post P1 andtip T1) to screen 42, thus allowing processor 41 to recognize a touch oftip T1 against the screen. Processor 41 is programmed to recognize atouch of tip T1 against screen 42 only in response to recognizing thatthe loop comprising left input port L, resistor R1, switch S1, resistorsR3 and R4, and output port MIC has opened (in response to opening ofswitch S1, which in turn occurs only when at least a threshold force isexerted on tip T1 to open the switch S1) and then, within thepredetermined time window, the conventional capacitive touch screensensing subsystem of screen 42 senses that tip T1 is in contact withscreen 42 (the latter event can occur only when switch S2 closes tocouple the capacitive load of cable 49's GND wire (which may include thecapacitance of host device 40) to screen 42 while tip T1 is in contactwith screen 42). Assembly A2 is comprised of switches S3, S4, spring 53,holder H2, post P2, and tip T2 and has exactly the same function asassembly A1 with the exception that the translation of shaft 46 istoward the right of the page.

Post P1 and “switch” S1 of FIG. 9 together constitute a switch, saidswitch being coupled to tip T1. Element S1 of this switch can simply bea node that is biased in a first position in so there is no contact withany stylus circuitry and can be moved by post P1 (as post P1 advances tothe right in FIG. 9) into electrical contact with contact point CP3 andtherefore be connected to GND. Also, post P2 and “switch” S3 of FIG. 9together constitute a switch, said switch being coupled to tip T2.Element S3 of this latter switch can simply be a node that is biased ina first position in contact with node M and can be moved by post P2 (aspost P2 advances to the left in FIG. 9) out of electrical contact withnode M.

In some embodiments, tip actuations that do not correspond to touchstrokes (e.g. the user provides sufficient actuation force to T1 or T2or in combination on surfaces other than the touch screen 42; hereinreferred to as “non-touch actuations”), the host software can be writtento interpret these events to indicate other types of user interactions.In some embodiments tip T2 non-touch actuations may be interpreted as“undo last stroke”. Likewise T1 non-touch actuations can be interpretedas “redo last stroke”. In other embodiments, such as when software onhost is serving to forward user interactions through host 40 to anetworked computer other than host 40, T1 non-touch actuations could beassigned to “left mouse click/release” and T2 non-touch actuations couldbe assigned to “right mouse click/release” events to be forwarded to thenetworked computer.

FIG. 10 is a block diagram of elements of an embodiment of the systemincluding stylus 200, capacitive touch screen device 201, and audiocable 260 coupled between stylus 200 and device 201. Device 201 includesstylus audio port set 240 (coupled to cable 260). Device 201 includeshost audio port set 204 (coupled to cable 260), a conventionalcapacitive touch screen 205, and processing circuitry coupled to touchscreen 105 and port set 204. The processing circuitry (referred toherein as a processor) includes a programmed processor 202,analog-to-digital conversion circuitry 208 coupled and configured togenerate (and assert to processor 202) digital audio data in response toan audio signal received at a microphone input port (labeled “MicAudio”) of port set 204, left channel digital-to-analog conversioncircuitry 206 coupled and configured to assert an analog audio signal toa left channel audio (“L audio”) output port of port set 204 in responseto audio data from processor 202 (or a memory associated with processor202), and right channel digital-to-analog conversion circuitry 207coupled and configured to assert an analog audio signal to a rightchannel audio (“R audio”) output port of port set 204 in response toaudio data from processor 202 (or a memory associated with processor202).

Stylus 200 includes conductive shaft 212, conductive, felted tip 210 atone end of the shaft, and another conductive, felted tip 211 at theother end of the shaft. Stylus 200 also includes passive switchedcircuitry (for indicating stylus mode), including switch 250 (coupledbetween tip 210 and shaft 212), switch 251 (coupled between tip 211 andshaft 212), sensor 220 (which can be implemented as a simple switchhaving two states or as a sensor having more than two states) andoptionally also filter 221 connected between the left channel (L) audioinput port (of port set 24) and an input of mixer 232, sensor 222 (whichcan be implemented as a simple switch having two states or as a sensorhaving more than two states) and optionally also filter 223 connectedbetween the right channel (R) audio input port (of port set 24) andanother input of mixer 232, and at least one sensor 230 (which can beimplemented as a simple switch having two states or as a sensor havingmore than two states) and optionally also filter 231 connected betweenone or both of the L and R audio input ports (of port set 24) and atleast one other input of mixer 232. Mixer 232 combines the outputs ofsensor 220 (or filter 221), sensor 222 (or filter 223), and sensor 230(or filter 231), and asserts the combined output to the Microphoneoutput port (of port set 24). The passive switched circuitry is coupledto the processor of device 201 via port set 240 and audio cable 260.

Alternatively, switches 250 and 251 are omitted from stylus 200, andreplaced by switch 252 (coupled between tip 210 and capacitance 213) andswitch 253 (coupled between tip 211 and capacitance 214). Capacitances213 and 214 may be internal to stylus 200 or external to (but coupledto) to stylus 200.

The switched circuitry of stylus 200 (implemented to include elements213, 214, 252, and 253) has a state (e.g., determined by switch 252 or253, each actuatable by force of contact of a tip of the stylus with anysurface, e.g., a touch screen) in which it couples a capacitive load(213 or 214) internal to the stylus to a tip of the stylus. The switchedcircuitry of stylus 200 (implemented to include elements 250 and 251 anda conductive shaft 212) has a state (e.g., determined by switch 250 or251, each actuatable by force of contact of a tip of the stylus with anysurface) in which it couples to a tip of the stylus an externalcapacitive load (e.g., connects the tip to conductive shaft 212 andthereby to the capacitance of a user's hand gripping the shaft 212).

The switched circuitry of stylus 200 also includes a switch or sensor(element 220) actuatable by a tip of the stylus to close or open acircuit path between a first audio output channel (of audio cable 260)and a microphone input channel (of cable 260) to allow routing of asignal (from host 201) back to the host either at full strength orattenuated in response (e.g., proportionally) to the contact force onthe tip. The switched circuitry of stylus 200 also includes switch orsensor (element 222) actuatable by a second tip of the stylus to closeor open a circuit path between a second audio output channel (of audiocable 260) and a microphone input channel (of cable 260) to allowrouting of a signal (from the host) back to the host either at fullstrength or attenuated in response (e.g., proportionally) to the contactforce on the second tip.

The switched circuitry of stylus 200 also includes at least one element230. Each element 230 is a switch (optionally with a filter 231connected in series therewith), or a variable circuit element (e.g., asensor or source), optionally with a filter 231 connected in seriestherewith, whose state is determined by sensor input (e.g., force,slider position, or position of a rotatable annular ring of stylus 200).For example, element 230 can be implemented as a sensor which is a bandpass filter, where the passband of such sensor is indicative of aparameter (e.g., width or color of a stroke by stylus 200 on screen 205)specified by a user by actuating a control (e.g., button, slider, orring) implemented by stylus 200. Each switch implementation of element230 has a subset of the functions of one type of variable sensorimplementation of element 230, in the sense that the switch has eitherof two states (open or closed, or 0 or 100%), whereas the sensor can beindicative of more than two states (e.g., a continuous range of levels).One type of sensor implementation of element 230 is (or includes or iscoupled to) a filter configured to filter an audio signal from host 201.The audio signal can be received from host 201 on the left audio channelof cable 260, or on the right audio channel of cable 260, or two audiosignals can be received from host 201: one by one sensor 230 from theleft audio channel of cable 260; the other by another sensor 230 fromthe right audio channel of cable 260.

When the filtered signal is returned to the host 201 (via mixer 232 andthe microphone channel of cable 260), the filtered signal can betransformed into digital data (in element 208 of host 201) and the datacan be processed by an appropriately programmed processor 202 in host201 to determine the output of the relevant sensor (and/or to identifywhich of several sensors in the stylus the signal is indicative of).

Processor 202 of FIG. 10 may generate through signal generation softwarelayer 209, and host 201 may then assert to stylus 200 over one or moreof the channels of cable 260, audio signals comprising frequencycomponents of multiple frequencies that are mixed together or as asingle frequency. These signals can be returned (looped back, withoptional filtering and attenuation) from elements 220, 221, 222, 223,230, 231, 232, and 240 to the host, or not returned to the host,depending on the state of passive switched circuitry in stylus 200. Forexample, signals asserted from host 201 to element 220 of stylus 200 onthe left audio channel of cable 260 can have a first frequency content(e.g., can comprise frequency components in a first band), signalsasserted from host 201 to element 222 of stylus 200 on the right audiochannel of cable 260 can have a different frequency content (e.g., cancomprise frequency components in a second band), and signals assertedfrom host 201 to one of elements 230 of stylus 200 on the left (orright) audio channel of cable 260 can have a different frequency content(e.g., can comprise frequency components in a third band). Or, signalsasserted from host 201 to elements 220 222, and 230 via cable 260 canall have the same frequency content, and each of filters 221, 223, and231 can be a band pass filter having a distinctive pass band, for easierdiscrimination processing (by host 201) of signals returned to the hostfrom mixer 232 and element 240 of stylus 200 in response to thesesignals.

In some implementations of the FIG. 10 system, switched circuitry ofstylus 200 presents a capacitive load (e.g., couples a capacitive loadthrough closed switch 250 or 251 and conductive material of shaft 212 ofthe stylus from a user's hand which grips the shaft, or couplescapacitor 213 or 214, or by direct connection to the GNDcontact whichuses the host device as the capacitance) to a tip (210 or 211) of thestylus in contact with touch screen 205 and thereby to conventionaltouch screen sensors (in or associated with screen 205) to cause thetouch screen to sense a “touch” event (“Event 1”). The switch whichpresents this load to the stylus tip may be biased to be open when lessthan a threshold force is exerted on the tip (e.g., by a capacitivetouch screen in contact with the tip). However, this in itself does notdisambiguate between a stylus tip touch and a finger (or hand) or othernon-stylus touch. Thus, the switched circuitry of stylus 200 preferablyincludes at least one other switch which, when closed (or opened in someembodiments) in a second event (“Event 2”), closes an open loop (oropens a closed loop in some embodiments) between stylus 200 and hosttouch screen device 201, said loop including a left or right audiooutput channel of cable 260 (connected between stylus 200 and host 201),circuit elements in stylus 200, and another channel (e.g., themicrophone channel) of cable 260. In response to Event 2, circuitry inthe touch screen device (e.g., audio circuitry 208 which is normallyused to process microphone input signals and processor 202) also sensesa “touch” event (and optionally also receives and recognizes the outputof one or more sensors and/or switches 220, 222, and 230 within stylus200). Processor 202 of touch screen device 201 is programmed tointerpret, as a stylus touch, the occurrence of “Event 1” within apredetermined time window (“x” seconds) of “Event 2.” The stylus may bephysically constructed to present “Event 1” or “Event 2” in eitherorder. Processor 202 is also programmed to interpret, as a non-stylustouch, the occurrence of “Event 1” that is not followed within x seconds(or not preceded by x seconds, in some embodiments) by an “Event 2.” Theduration of the window “x seconds” is preferably predetermined in amanner that depends on expected processing delays (e.g., the delayinherent in any required processing of the signals, such as a Fouriertransform, sensed by touch screen device 201 including its screencircuitry and its audio circuitry).

In the second class of embodiments, the capacitive touch stylus has atleast a first mode of operation and a second mode of operation, andincludes at least one conductive tip (each, preferably, a conductivefelted tip) and passive switched circuitry including at least one switch(e.g., one or more of the switches of the switched circuitry of stylus45 of FIG. 9, or element 220 or 222 (implemented as a switch) of FIG.10, or switch 250, 251, 252, or 253 of FIG. 10), biased in a defaultstate indicative of the first mode of operation but switchable into asecond state indicative of the second mode of operation in response tomovement of the tip, where the switch is coupled to the tip in one ofthe default state and the second state. Typically, movement of the tipin response to exertion of not less than a threshold force on the tip(e.g., by a touch screen in response to user-exerted pushing force onthe stylus against the screen) is required to transition the switch fromthe default state to the second state. The switched circuitry alsoincludes a stylus audio port set (e.g., stylus audio port set 240 ofFIG. 10, or the stylus audio port set comprising ports L, R, MIC, andGND of FIG. 9) including at least one audio port configured to becoupled to an audio cable (e.g., cable 49 of FIG. 9). In typicalembodiments in the second class, the stylus audio port set includes atleast one audio input port (e.g., left channel input audio port L orright channel input audio port R of FIG. 9), and at least one audiooutput port (e.g., microphone port MIC of FIG. 9), and optionally also aground port (e.g., ground port GND of FIG. 9). Preferably, the stylusaudio port set is configured to be coupled to an end of a conventionalaudio cable (e.g., cable 49 of FIG. 9) including left and right outputchannel connectors, a microphone channel connector, and a groundconnector, so that another end of the cable can be coupled to an audioport set (referred to herein as a “host audio port set”) of a touchscreen device, where the touch screen device includes an audio subsystemincluding the host audio port set, and the host audio port set (e.g.,host audio port set 204 of FIG. 10, or the host audio port setcomprising ports L′, R′, MIC′, and GND′ of FIG. 9) typically includesleast two audio output ports (configured to assert left and right outputaudio channels), an audio input port (configured to receive an audioinput from a microphone), and a ground port.

Typically, the first mode of operation is use of the stylus with its tipin contact with a capacitive touch screen (or other object) with notless than a threshold force being exerted by the object on the tip, andthe second mode of operation is other use of the stylus (e.g., use withthe tip in contact with an object with less than the threshold forceexerted by the object on the tip). For example, stylus 45 of FIG. 9 hasa first mode of operation (in which tip T2 is pressed against screen 42with force sufficient to translate post P2 far enough (and withsufficient velocity) to open switch S4 and then to close switch S3within a predetermined time window after switch S4 opens). Processor 41(of device 40 of FIG. 9) is programmed to recognize that stylus 45 is inthis state in response to determining that the loop comprising the rightchannel conductor of cable 49 (and resistor R5, capacitor C1, and switchS4 of the switched circuitry of stylus 45) has transitioned from aclosed to an open state, and then receiving from touch screen 42 (withinthe predetermined window) an indication of a touch on screen 42.Processor 41 assumes that stylus 42 is in the second mode of operationuntil transitions in the states of switches S3 and S4 of stylus 45 occurwith the appropriate timing to cause processor 41 to recognize thatstylus 45 is in the first mode of operation. With stylus 45 in the firstmode of operation, a further change in state of one (or both) ofswitches S3 and S4 is recognized by processor 41 as entry of stylus 45into its second mode of operation.

In other typical embodiments in the second class (e.g., those in whichthe stylus has a conductive shaft that couples the capacitance of ahuman gripping the shaft to switched circuitry within the shaft), thefirst mode of operation is use of the stylus with its tip in contactwith a capacitive touch screen (or other object) with not less than athreshold force being exerted by the object on the tip and the stylusgripped by a user (such that not less than a threshold capacitance iscoupled by switched circuitry from the user to the tip), and the secondmode of operation is other use of the stylus (e.g., use with the tip incontact with an object with less than the threshold force exerted by theobject on the tip, or with less than the threshold capacitance coupledfrom to the tip).

In some typical embodiments in the second class (e.g., in operation ofstylus 45 of above-described FIG. 9), the first mode of operation is useof the stylus with occurrence of two events within a predetermined timewindow: a threshold capacitance is coupled to the tip (e.g., acapacitance internal to the stylus, e.g., capacitance 213 or 214 whichis internal to stylus 200 of FIG. 10, or external to the stylus butcoupled to the stylus by the switched circuitry, e.g., the capacitanceof cable 49 of FIG. 10) in response to exertion of not less than athreshold force on the tip (e.g., by a capacitive touch screen or otherobject in contact with the tip, as the tip is forced against theobject); and a signal is asserted (e.g., for transmission via an audiocable or other wired link, or a wireless link, to a touch screen device)other than by coupling a capacitance to the tip, but in response toexertion of force on the tip (e.g., by a capacitive touch screen orother object in contact with the tip). In these embodiments, the secondmode of operation is other use of the stylus (e.g., use with occurrenceof one but not both of these events, or with both of the eventsoccurring but not within a predetermined time window). The predeterminedtime window is typically sufficiently wide to allow processing circuitryin a host device (e.g., processor 202 of touch screen device 201 of FIG.10, or processor 41 of touch screen device 40 of FIG. 9) to recognizeand distinguish between the two events, but sufficiently short so thatboth events occur in response to a single touch of the stylus on acapacitive touch screen by a user who intends to indicate information tothe touch screen device.

In some embodiments in the second class (e.g., stylus 200 of FIG. 10including elements 250 and 251, and with shaft 212 being a conductiveshaft), the stylus has a conductive tip (e.g., a conductive, felted tip)that is continuously coupled to a sufficient capacitance (when a humanuser grips the stylus) to allow a capacitive touch screen device torecognize (as a touch) simple contact of the tip on the screen of thetouch screen device, and the switched circuitry has a first state whichallows the stylus to assert to the touch screen device (e.g., forwardto, or loop back from, the touch screen device) a signal (when thestylus is coupled by an audio cable or other link to the touch screendevice) that indicates to the touch screen device that the screen (oranother object) is exerting at least a threshold force on the stylustip. The switched circuitry also has a second state which prevents thestylus from asserting such signal to the touch screen device, therebyindicating to the touch screen device that the screen (or other object)is not exerting force (or is exerting less than the threshold force) onthe stylus tip.

In some embodiments in the second class, the stylus has a firstconductive tip at one end (e.g., a conductive felted tip), and a secondconductive tip at another end (e.g., another conductive felted tip). Thefirst conductive tip (e.g., at a “writing” end of the stylus) isconfigured to be moved into a position causing the switched circuitry toenter a first state coupling a capacitance to the tip and closing a loopbetween a first input port (e.g., a left audio channel input port) ofthe stylus audio port set and at least one output port of the stylusaudio port set, where the capacitance is sufficient to allow acapacitive touch screen device (e.g., a conventional capacitive touchscreen device) to recognize (as a touch) simple contact of the firstconductive tip on the screen of the touch screen device. Preferably, theswitched circuitry is implemented so that both these events (coupling ofthe capacitance to the first conductive tip, and opening(open-circuiting) the loop between the first input port and at least oneoutput port of the stylus audio port set) occur within a predeterminedtime window. In response to the first conductive tip being in anotherposition, the switched circuitry enters a second state decoupling thecapacitance from said first conductive tip and/or closing the loopbetween the first input port and said at least one output port of thestylus audio port set. The second conductive tip (e.g., at an “erasing”end of the stylus) is configured to be moved into a position causing theswitched circuitry to enter a third state coupling a capacitance to thetip and closing a loop between a second input port of the stylus audioport set (e.g., a right audio channel input port) and at least oneoutput port of the stylus audio port set, where the capacitance issufficient to allow a capacitive touch screen device (e.g., aconventional capacitive touch screen device) to recognize (as a touch)simple contact of the second conductive tip on the screen of the touchscreen device. Preferably, the switched circuitry is implemented so thatboth these events (coupling of the capacitance to the second conductivetip, and opening (open-circuiting) the loop between the second inputport and said at least one output port of the stylus audio port set)occur within a predetermined time window. In response to the secondconductive tip being in another position, the switched circuitry entersa fourth state decoupling the capacitance from the second conductive tipand/or closing the loop between the second input port and said at leastone output port of the stylus audio port set.

In some embodiments, the invention is a system including a stylus (whichbelongs to the second class of embodiments), a touch screen devicehaving an audio subsystem (including a host audio port set of the typementioned above) and a processor coupled to the audio subsystem, and anaudio cable connected between the stylus audio port set of the stylusand the host audio port set of the touch screen device, wherein theprocessor of the touch screen device is configured to recognize anoperating mode of the stylus in response to at least one response signalreceived at the host audio port set in response to assertion of at leastone signal from the audio subsystem via the host audio port set and thecable to the stylus audio port set.

In some embodiments, the state of the stylus audio port set (e.g., inresponse to the state of the host stylus audio port set) is indicativeof one or more of: contact between a tip of the stylus and a touchscreen (or other object); pressure exerted by a touch screen (or otherobject) on a tip of the stylus; state of at least one sensor of theswitched circuitry (e.g., element 220, 222, or 230, implemented as asensor, of FIG. 10); and state of at least one switch (e.g., element220, 222, or 230, implemented as a switch, of FIG. 10) of the switchedcircuitry. In some such embodiments, the switched circuitry includes atleast one filter coupled and configured to filter at least one signalreceived from a touch screen device (via an audio cable) at the stylusaudio port set, thereby generating a filtered signal, and the switchedcircuitry is configured to assert the filtered signal at the stylusaudio port set (for transmission to the touch screen device (via theaudio cable).

Typical embodiments in the second class provide a means forcommunicating mode information from a stylus to a host that allows thehost to distinguish between intended touches of the stylus (on acapacitive touch screen) and other touches not intended to be strokes orother kinds of drawing/writing information (such as erasures). Ratherthan to assert mode information actively from a locally powered (active)stylus (including powered sensors and/or switches for determining andasserting the mode information) via wireless communication to or directstimulation of the host, preferred embodiments of the invention usepurely passive switched circuitry in a stylus to assert mode informationto a host via a conventional audio port set conventionally present inthe host and a cable coupled between the stylus and the host. Thesepreferred stylus embodiments do not pulse or otherwise communicate anyinformation through a stylus tip other than simple contact (which isrecognizable in a conventional manner by a conventional touch screendevice).

In a third class of embodiments of the stylus, the stylus has aconductive tip (e.g., a conductive, felted tip) and includes passiveswitched circuitry having a first state which couples a capacitance tothe tip, where the capacitance is sufficient to allow a capacitive touchscreen device (e.g., a conventional capacitive touch screen device) torecognize (as a touch) simple contact of the tip on the screen of thetouch screen device, and a second state which decouples the capacitancefrom the tip, thereby preventing the touch screen device fromrecognizing (as a touch) simple contact of the tip on the screen. Forexample, stylus 45 of FIG. 9 includes passive switched circuitry havinga first state (in which switch S2 or S4 is closed) in response to a tip(T1 or T2) being pressed against screen 42 with force sufficient totranslate post P1 (or P2) far enough away from its default position toclose switch S2 or S4. The switched circuitry of stylus 45 of FIG. 9also has a second state (in which both switches S2 and S4 are open) inresponse to neither of tips T1 and T2 being pressed against screen 42with force sufficient to translate post P1 (or P2) far enough away fromits default position to close switch S2 or S4.

In some embodiments in the third class (e.g., in the FIG. 9 embodiment),the capacitance is a capacitive load external to the stylus (i.e., thecapacitive load of cable 49 coupled to stylus 45). Alternatively, thecapacitance can be internal to the stylus (e.g., capacitance 213 or 214of implementations of stylus 200 of FIG. 10 that include elements 213,214, 252, and 253). Typically, the passive switched circuitry (ofembodiments in the third class) includes at least one switch biased in adefault state (e.g., the default state of switch S2 or S4 of FIG. 9)which couples the capacitance to (or decouples the capacitance from) thetip but is switchable into a second state (which decouples thecapacitance from (or couples the capacitance to) the tip in response tomovement of the tip (typically, movement of the tip in response toexertion of not less than a threshold force on the tip, e.g., by a touchscreen in response to user-exerted pushing force on the stylus againstthe screen), where the switch is coupled to the tip in one of thedefault state and the second state. The switched circuitry also includesa stylus audio port set (e.g., port set 240 of FIG. 10, or ports L, R,MIC, and GND of FIG. 9) including at least one audio port configured tobe coupled to an audio cable. In typical embodiments in the third class,the stylus audio port set includes at least one audio input port, and atleast one audio output port, and optionally also a ground port.Preferably, the stylus audio port set is configured to be coupled to anend of a conventional audio cable (e.g., cable 49 of FIG. 9) includingleft and right output channel connectors, a microphone channelconnector, and a ground connector, so that another end of the cable canbe coupled to an audio port set (referred to herein as a “host audioport set”) of a touch screen device, where the touch screen deviceincludes an audio subsystem including the host audio port set, and thehost audio port set typically includes least two audio output ports(configured to assert left and right output audio channels), an audiooutput port (configured to receive an audio input from a microphone),and a ground port.

In various embodiments, the stylus is a powered, non-powered, active, orpassive device. For example, it is contemplated that some embodiments ofthe stylus are (e.g., the switched circuitry thereof is) speciallydesigned to draw power (e.g., about one half of a Watt) from an audiooutput channel (and/or other channels) of a cable connected between thestylus and a host, for use by op amps or other circuit elements in thestylus. In operation, other embodiments of the stylus would not drawpower from a host (or would draw no more than an insignificant amount ofpower from a host, e.g., no more than very small amounts of powerunavoidably dissipated as heat due to resistance of circuit elements inthe stylus).

In some embodiments, the stylus for a capacitive touch screen isconfigured to mechanically stimulate the touch screen and to assertmodal information to the touch screen by patterned disconnection of acapacitive load (either external to the stylus, e.g., provided by thebody of a human gripping the stylus, or internal to the stylus) viapurely mechanical means of winding or shaking. For example, the stylusis capable of being powered (e.g., re-charged) in response to a shaking,twisting, or general user motion by means of an internal mechanism thattranslates the mechanical energy into electrical energy (e.g., forrecharging a battery local to the stylus, or for use directly by thestylus for its operation). The touch screen is configured to implement amethod for recognizing such a stimulus pattern to select a modality ofinteraction with the stylus.

In some embodiments, the stylus is configured to stimulate a capacitivetouch screen mechanically and to communicate modal information to thetouch screen (e.g., by patterned disconnection of circuitry within thestylus) via a wireless link (e.g., an RF link), where power consumed bythe stylus during operation is derived from mechanical means local tothe stylus (e.g., within the stylus), e.g., by shaking or twisting thebody of the stylus. The touch screen is configured to implement a methodfor recognizing such a stimulus pattern to select a modality ofinteraction with the stylus.

In some embodiments, the stylus is configured to stimulate a capacitivetouch screen mechanically and to communicate (to the touch screen)stylus identification data that uniquely identifies the stylus (or auser thereof). The touch screen device is configured (e.g., includes aprocessor programmed with application software) to identify the stylus(or user) in response to the stylus identification data, e.g., so thatthe touch screen device can operate in different modes in response toinput from each of multiple styli. For example, the touch screen deviceimplements an annotation application that uses a unique identificationof each stylus to identify a unique user and to capture and/or displaythe user's name and or other specific information that is tied to thatuser.

In some embodiments (e.g., some implementations of device 40 of FIG. 9and some implementations of device 201 of FIG. 10), the capacitive touchscreen device is configured to recognize (e.g., processor 41 of FIG. 9,or processor 202 of FIG. 10, is programmed to recognize) an operatingmode of an embodiment of the stylus (e.g., stylus 45 of FIG. 9 or stylus200 of FIG. 10) in response to at least one signal indicative of thestate of switching circuitry in the stylus, and in response to touchscreen sensor data (i.e. data generated and processed conventionally intouch screen devices to calculate a centroid from an outline of anobject's contact area on a touch screen) including by processing thetouch screen sensor data in at least one of the following ways:recognizing movement of the stylus on the screen and predicting a futurelocation of contact area of the stylus on the screen (e.g., bydetermining a sequence of centroids of outlines of the moving stylus'scontact areas on the touch screen and projecting a next centroid fromthe sequence); determining velocity of contact area of the stylus on thescreen; and determining size of contact area of the stylus on thescreen. This can allow (or help to allow) the touch screen device todisambiguate between user-intended stylus touches on the screen andnon-intended or spurious touches. For example, the touch screen devicemay be configured to recognize a touch on the screen as an intendedstylus touch only in response to receiving a signal indicative of thestate of switching circuitry in the stylus within a predetermined timewindow of determining (from the touch screen sensor data) that adetected touch on the screen occurs at a location matching a predictedfuture location of a moving stylus on the screen.

FIG. 11 is a flow chart of steps performed in operation of an embodimentof the stylus and a capacitive touch screen device (e.g., by stylus 200and touch screen device 201 of FIG. 10). At step 601, the devicedetermines if the stylus is or may be present (e.g., in a conventionalmanner using conventional capacitive touch screen sensors associatedwith the device's touch screen to sense a touch on the screen). If it isdetermined that a stylus is or may be present, the device (e.g., device210) asserts (in step 602) audio signals (e.g., a set of N distinctsignals) over left and right audio channels of a cable coupled betweenthe stylus and the device (e.g., device 201 asserts audio signal toleft, “L”, and right, “R”, audio output ports of port set 204 fortransmission to stylus 200 over left and right channels of cable 260).If the device determines that the stylus is no longer present (in step603), it ceases to assert the audio signals (step 604). If the devicedetermines that the stylus continues to be or may be present (in step603), it reads and processes (in step 605) the signal received at aninput audio port (e.g., device 201 reads and processes the signalreceived from stylus 200 via cable 260 at the microphone input port ofport set 204). If a return signal is determined (in step 606) to havebeen received at the input audio port (e.g., because switch 220 or 222is closed in response to sufficient actuation force exerted by touchscreen 205 on tip 210 or 211 of stylus 200), the device (e.g. processor202 of device 201) decodes the return signal and sends a correspondingmessage (determined by the decoded return signal) indicative of styluspresence at the screen (and optionally also indicative of at least onecharacteristic of a stroke by the stylus on the screen) to anapplication layer (e.g., of software executed by processor 202) and thedevice then repeats step 603 to continue to monitor whether the stylusis present. If a return signal is not determined (in step 606) to havebeen received at the input audio port, the device repeats step 603 tocontinue to monitor whether the stylus is present.

FIG. 12 is another flow chart overview of steps performed in operationof an embodiment of the stylus and a capacitive touch screen device(e.g., by stylus 200 and touch screen device 201 of FIG. 10). At step501, the device (e.g., processor 202 of device 201) is receptive to data(messages) from the device's touch screen (e.g., data generated in aconventional manner using conventional capacitive touch screen sensorsassociated with the touch screen to sense a touch on the screen) andfrom the stylus (e.g., via cable 260). If the device determines (in step503) that a stylus (an embodiment of the stylus) is not present, thedevice (in step 502) assumes that any touch sensed by the touch screenis by a human finger (or other object that is not an embodiment of thestylus) and operates conventionally (e.g., by producing a display.

If the device determines in step 503 (e.g., by receiving a return signalon cable 260 in response to an audio signal asserted on the left channeland/or the right channel of cable 260) that a stylus (an embodiment ofthe stylus) is present, the device (in step 504) continues to bereceptive to data (messages) from the device's touch screen (e.g., datagenerated in a conventional manner using conventional capacitive touchscreen sensors associated with the touch screen to sense a touch on thescreen) and from the stylus (e.g., via cable 260).

If the device then determines in step 505 (e.g., by failing to receive areturn signal on cable 260 in response to an audio signal asserted onthe left channel and/or the right channel of cable 260) that a stylus isnot present, it returns to step 501. If the device determines in step505 that a stylus is present, the device proceeds to perform one or moreof steps 506, 508, 510, and 512.

If the device determines in step 506 (e.g., by recognizing an indicationof a touch on the touch screen from conventional touch screen sensorsassociated with the touch screen, without any accompanying change instatus of a return signal from the stylus via cable 260) that there hasbeen a touch on the screen by a stylus (i.e., an embodiment of thestylus), it operates (in step 507) by producing a display in response tothe touch (without modifying the display in response to any modalmodifier).

If the device determines in step 508 there has been a touch on thescreen by a first tip of an embodiment of the stylus (e.g., byrecognizing occurrence of two events within a predetermined time window:an indication of a touch on the touch screen from conventional touchscreen sensors associated with the touch screen; and a change in statusof a return signal from the stylus via cable 260 indicative of a touchby the first tip of the stylus, where the first tip may be a “marking”tip of the stylus), it operates (in step 509) by producing a display inresponse to the touch (optionally in a manner modified in response to atleast one modal modifier received from the stylus, e.g., via cable 260from a sensor 230 of the stylus).

If the device determines in step 510 there has been a touch on thescreen by a second tip of an embodiment of the stylus (e.g., byrecognizing occurrence of two events within a predetermined time window:an indication of a touch on the touch screen from conventional touchscreen sensors associated with the touch screen; and a change in statusof a return signal from the stylus via cable 260 indicative of a touchby the second tip, where the second tip may be an “erasing” tip of thestylus), it operates (in step 511) by producing a display (e.g., erasinga previously displayed mark on the screen) in response to the touch(optionally in a manner modified in response to at least one modalmodifier received from the stylus, e.g., via cable 260 from a sensor 230of the stylus).

If the device determines in step 512 there has been a touch on thescreen by an unidentified tip of an embodiment of the stylus (e.g., byrecognizing occurrence of two events within a predetermined time window:an indication of a touch on the touch screen from conventional touchscreen sensors associated with the touch screen; and a change in statusof a return signal from the stylus via cable 260 indicative of a touchby at tip of the stylus), it operates (in step 513 or 514) by producinga display in response to the touch (e.g., with the assumption that thetouch is intended to cause display of a mark rather than to erase apreviously displayed mark, unless the touch is accompanied by a modalmodifier indicating an erasure) in a manner modified in response to anymodal modifier(s) received from the stylus, e.g., via cable 260 from atleast one sensor 230 of the stylus), and then returns to step 504.Specifically, the device produces the display (in step 513) in a mannermodified in response to at least one modal modifier received from thestylus, or the device produces the display (in step 514) an unmodifiedmanner (e.g., a default manner) if no modal modifier received from thestylus.

In some embodiments, the tip actuation signals from the stylus to thehost device may be provided to the host device through, for example, theDOCK connector of a host device that provide power to the stylus fromthe host device (the DOCK connector is a docking connector that hasmultiple signals in it: audio, USB, RS232, etc). The tip actuationsignals may also be provided through a USB connection (that is also mayprovide power to the stylus from the host device) through a USB cable.The tip actuation signal may be provided to the host device utilizingany data communications protocol (e.g., RS232, WiFi, BlueTooth, CAN,etc.); if it is a wireless protocol, then stand-alone power source(e.g., battery) is needed. An aspect of the tip-to-touch disambiguationalgorithm relies on a data communications means, either parallel orserial, that is capable of representing and transmitting the followingevents in at least one direction (from the stylus to the host device) ina timely manner:

TIP(n) depressed (i.e., sufficient force applied)

TIP(n) released (insufficient force applied)

wherein n represents the tip number.

FIG. 13 is a detailed state diagram that is illustrative of datagathering and processing techniques (summarized in FIG. 12) useful inclassifying touches or strokes on the capacitive touch screen intovarious types of strokes such as stylus/tip, finger or palm touchesaccording to an embodiment of the invention. It describes in detail aspecific “time window disambiguation” technique to properly identifywhich tip events correspond to the stroke events. It is not the onlytechnique capable of stroke classification. There are others that may beused and that are known to those of ordinary skill in the art.

FIG. 13 contains seven states:

-   -   Initialize Unclassified Stroke List 610;    -   Wait for Tip Down Event 612;    -   Wait for End Touch 614;    -   Wait for Tip Up 616;    -   Wait for New Touch Stroke 618;    -   Gather Strokes 620;    -   Wait for End 622.

FIG. 13 contains the description of the events and transitions thatoccur from state to state, and the interrelationship between states.

In the FIG. 13 state diagram, all active timers are stopped on theirexpiry or on transition to a new state. On FIG. 13, the prefix “E: . . .” denotes finite state machine entry actions into states (to be executedeven if the state vectors to itself.). The prefix “T: . . . ” denotesfinite state machine transition actions. In certain embodiments,TMR_WAIT_FOR_TOUCH is approximately 200 msecs. TMR_GATHER_STROKES isapproximately 100 msecs. TMR_EXPECT_TIP is approximately 200 msecs.

The stylus must ultimately provide information to the softwareapplications on the host, typically the capacitive touch screen deviceitself. It is possible that the capacitive touch screen device is aclient to another host. Even though the present description does notexplicitly describe that configuration, the stylus stroke classificationtechnique is still applicable even when the processing takes place onanother device. While there are many applications that may use thestylus, the most common applications are electronic annotation, notetaking, or drawing software running on the host device. It is useful forthese applications have each stroke classified into four distinctcategories: “STROKE_UNCLASSIFIED” which is a temporary state denotingthat the algorithm does not yet have enough information to determine thestroke type; “TIP_STROKE(n)” (where n denotes the unique tip thatoriginated the event) which denotes that the stroke has beensuccessfully categorized as a having been generated by a tip interactingwith the touch screen; “FINGER_STROKE” which indicates that the strokewas generated by the user's finger; and “PALM_STROKE” which identifiesthe stroke as a spurious un-intentional stroke that was created by thepalm touching the surface or other non-intended user stroke.

The time window technique (e.g., processing strokes by comparing thetime of the event to a predetermined time interval that starts upon T1the transition from stylus tip up to tip down) alone does not ultimatelyserve to fully classify all strokes as there may be multiple strokeevents that begin within the time window of T_(window) seconds betweenthe occurrences of the tip down events and touch start events; more thanone touch event may start within that window (e.g., the user's palm andthe stylus touch the surface within the same time window). Theclassification or disambiguation described with reference to the FIG. 13finite state machine relies on two algorithms to further disambiguatethe strokes called “PROCESS UNCLASSIFIED STROKES” which may or may notarrive at a final classification of all strokes as new touch locationsare processed by the algorithm; and “FORCE CLASSIFICATION” which forcesthe election of a single stroke to be classified as a TIP_STROKE, whileclassifying all others as PALM_STROKEs.

Definition of terms. A stroke as referred to in this embodiment isdefined as an ordered set of points, (corresponding to the contactlocation on the touch screen) including the timestamp for when the pointwas captured by the host device. Thus, a stroke is an ordered sequenceof ordered pairs {[(x₁, y₁), t₁], . . . [x_(n), y_(n)), t_(n)]}, where,for all i from 1 to n, (x_(i), y_(i)) is the two-dimensional location ofthe ith point corresponding to the contact location recorded at timet_(i). For any i from 1 to n−1, the ith stroke segment is defined as theline segment connecting two consecutive point locations of the stroke(x_(i), y_(i)) to (x_(i+1), y_(i+1)). The stroke path is the connectedpolygonal path connecting the point locations of the stroke. A centroidof the stroke is defined as the center of mass of the collection ofpoint locations of the stroke.

The process “PROCESS UNCLASSIFIED STROKES” is executed for eachunclassified stroke in the set of unclassified strokes gathered by thefinite state machine above. These strokes represent the possible tipgenerated strokes (referred to as “tip strokes” as compared with palmgenerated strokes (referred to as “palm strokes”)). It is known that tipstrokes exhibit a set of characteristics that are distinguishable fromthe set of characteristics exhibited by palm strokes. This processconverges on selecting one stroke from among the set of strokes that isthe likeliest to be the tip stroke by a set of heuristics thatdifferentiate between the two sets of palm stroke characteristics andtip stroke characteristics. The process establishes a continuallyupdated probability for each stroke in the set of unclassified strokesbased on the heuristics detailed below. Once a probability that a strokeis a tip stroke reaches 0, or some threshold value close to zero, thatstroke is immediately assigned as a palm stroke and removed from the setof unclassified strokes. If only one stroke remains in the set, then itis classified as the tip stroke and the process is complete. For eachstroke in the set of unclassified strokes there are two types datapoints that can be appended to the stroke based on continued tracking ofthose strokes: “stroke is moving” (which results in a new segment of thestroke path to be appended to the existing stroke path, and “stroke hasended” (resulting from the tip and or palm having been lifted fromcontact with the touch screen). “PROCESS UNCLASSIFIED STROKES” isexecuted as soon as the strokes are gathered (as shown in the finitestate machine of FIG. 13), and each time a new data point [(x_(i),y_(i)), t_(i)] is added to the end of the stroke sequence. The finitestate machine will have already eliminated all possible strokes that donot fall into the previously described time window, and new strokes thatmay occur outside of that time window are not added to the set ofunclassified strokes, but instead immediately classified as palmstrokes.

The first time “PROCESS UNCLASSIFIED STROKES” is executed (i.e. afterthe transition from “ST_GATHER_EVENTS”), for each stroke in the set ofunclassified strokes, the initial probability that the stroke should beclassified as a tip stroke is generated by determining the accelerationbetween the end of the previously classified tip stroke and applying amathematical function to calculate an approximation that the probabilitythat the stroke is a tip stroke. The beginning point of each stroke iscompared to the ending point of the last categorized tip stroke todetermine an acceleration vector with magnitude, a. The “accelerationprobability function” is applied to calculate an approximation for theprobability that the stroke is a tip stroke. If there is no previous tipstroke then the probability is assigned to 1.

A piecewise linear acceleration probability function such as thefollowing may be used to calculate an approximation for the probabilitythat a stroke is a tip stroke:

$\begin{matrix}{{P(a)} = {{1{\mspace{14mu} }{if}\mspace{14mu} a} < {{threshold}\mspace{14mu} A_{1}}}} \\{= {{{\left( {A_{2} - a} \right)/\left( {A_{2} - A_{1}} \right)}\mspace{14mu} {if}\mspace{14mu} a}>={{threshold}\mspace{14mu} A_{1}\mspace{14mu} {and}}}} \\{{a < {{threshold}\mspace{14mu} A_{2}}}} \\{= {0\mspace{14mu} {{otherwise}.}}}\end{matrix}\mspace{14mu}$

This function establishes three ranges. Below a certain accelerationvalue A₁, the probability that the stroke is a tip stroke is one; aboveor equal to A₁, but below A₂, the probability that the stroke isgenerated by the tip decreases linearly to zero. For accelerations abovepoint A₂ the probability that the stroke is a tip stroke is zero. Thisprocessing allows us to use a model of human hand motion assuming thatthere is a maximum acceleration that can be achieved by the at the tipof a stylus held by an average human hand during writing; and that, asthe acceleration rises, the likelihood that the stroke was generated bya stylus tip held by a human hand decreases to zero according to thefunction above.

Differentiable (i.e., smooth) functions whose general shape resemblesthe piecewise linear acceleration probability function may also be usedto approximate the probability that a given stroke is a tip stroke. Oneexample is a logistic function such as

P(a)=[1/(1+êa)]+[(A ₁ +A ₂)/2],

where e is the base of the natural logarithm.This logistic function has asymptotes at P=0 and P=1 rather than fixingboundaries for when the probability is exactly zero or one.

For each segment in each unclassified stroke, the process refines theprobability based on the following techniques:

-   -   Velocity thresholding: the velocity ν of a stroke segment is        calculated, and ν is used in a mathematical function to        calculate an approximation for a probability that the stroke is        a tip stroke. For example, if velocity ν is greater than the        threshold V₁, then the stroke can be immediately assigned a        probability of zero. All probabilities are accumulated by        multiplying the last calculated probability by the new        calculated probability. In this case any stroke segment with        velocity greater than V₁ would immediately be given a        probability of zero, and therefore the whole stroke would be        classified as a palm stroke. A decreasing, differentiable        function of ν can also be used to determine if the probability        of a given stroke is a tip stroke. One possibility is an        exponential decay function such as

P(ν)=bê(rν),

-   -   where e is the base of the natural logarithm, b is positive, r        is negative, and b and r are determined through statistical        methods on a large data sample. In this case any stroke segment        with velocity greater than some value based upon b and r, would        be given a probability close to zero, thereby increasing the        probability that the whole stroke would be classified as a palm        stroke. If the data sample suggests a more complicated function        is required, a suitable function will be chosen for the velocity        probability function.    -   Acceleration Probability: the “Acceleration probability        function” is applied to the acceleration derived from the        distance and time between the ending point of the stroke, and        the distance and time of the previous point in that stroke        (e.g., the last segment of acceleration). All probabilities are        accumulated by multiplying the last calculated probability by        the new calculated probability. Any stroke that achieves a        probability of zero or is below some threshold value close to        zero is immediately classified as a palm stroke. The accumulated        probability is known as Pa.    -   The process “FORCE CLASSIFICATION” is run once as (shown by the        finite state machine in FIG. 13). It is executed once the tip is        released AND there is more than one stroke remaining in the set        of unclassified strokes. This process will choose the stroke        most likely to be a tip stroke based on the accumulated        probabilities of the steps above and the following techniques:    -   First, any strokes that are still active (i.e., not ended)        within a time interval similar to the time interval (i.e.,        T_(window)) used to determine that a stroke was possibly a tip        stroke must immediately be classified as a palm stroke. If only        one stroke remains in the set then it is classified as the tip        stroke and the process is complete.    -   If more than one stroke remains, for each unclassified the        following 3 techniques further refine the probabilities        calculated by the “PROCESS UNCLASSIFIED STROKES” process.        -   Median Stroke Segment Lengths: For each segment in each            unclassified stroke, calculate the median length of all            stroke segments of a stroke. Calculate probability “Pm” by            assigning the ratio of each of the median values to the            maximum median value of all remaining unclassified stroke            medians. This will assign a higher probability to all            strokes with a higher median length. It is contemplated that            using the median absolute deviation from the median (i.e.,            the MAD) or other statistic may also be similarly used.        -   Dead Reckoning: Calculate a motion vector from up to 2            previously completed tip strokes that have all occurred            within a time interval T prior to the starting time of the            stroke being analyzed. If less than two strokes exist that            meet that criteria, then assign probability “Pd” to 1.            Otherwise, for each stroke that meets the criteria calculate            a measure of the location or center (e.g., centroid) of each            stroke. Use the two locations to calculate the velocity            vector between them. Then calculate a point that would be            the next point in sequence given a constant velocity. This            gives the “dead reckoning point” for where the next tip            stroke would be expected to be. Calculate the location or            center (e.g., centroid) of each unclassified stroke.            Calculate probability Pd of the location u of an            unclassified stroke as

Pd(c)=1−(u−d)/s

-   -   -   where d is the dead reckoning point and s is the sum of all            distances between each unclassified stroke center and the            dead reckoning point. This will assign a higher probability            Pd to the unclassified strokes with points (or centers) that            are closest to the dead reckoning point.        -   Current Palm Placement: if any strokes previously classified            as palm strokes are currently still active (i.e., an object            is still in contact with the host device), calculate            centroids (or other measure of the location) of each of            those strokes. Calculate the centroid of all the centroids            of the different active palm strokes. For each unclassified            stroke, calculate the probability

Pp=(c−u)/s

-   -   where c is the centroid of palm centroids, u is the start of the        unclassified stroke, and s is the sum of all distances from each        unclassified stroke starting point to the centroid of palm        centroids. This will assign a higher probability to each of the        strokes that started furthest from the current palm centroid of        centroids.        Once Pd, Pm, and Pp have been calculated, for each unclassified        stroke, apply the following formula:

Ptip=Pa*W1+Pd*W2+Pm*W3+Pp*W4

-   -   Where (W1+W2+W3+W4)=1 and W1 through W4 represent a weight        between zero and one (inclusive) given to each probability.        The stroke with the highest probability (Ptip) value is        classified as a tip stroke. All others are classified as palm        strokes.

It is contemplated that more sophisticated statistical methods can beapplied to increase the reliability of the calculations for theindividual probability functions Pa, Pd, Pm and Pp. Samples of data canbe collected and analyzed using statistics to estimate the shape of theprobability functions including the class or type of function and theparameters specific for each function.

It is contemplated that mechanical switches, on occasion, may beactuated so fast by hand movements that brief tip up/tip down events maybe lost. The finite state machine of FIG. 13 assumes no loss of events.Refinements are contemplated that can take this loss of events intoconsideration based upon proximal distance and time from the lastrecognized stroke.

It should be understood that while some embodiments of the presentinvention are illustrated and described herein, the invention is definedby the claims and is not to be limited to the specific embodimentsdescribed and shown.

1. A stylus comprising: a felted tip having a deformable conductivesurface for contacting a capacitive touch screen, the tip having acontact area sufficient in magnitude and the tip is coupled to acapacitance sufficient in magnitude to cause the capacitive touch screento recognize a touch by the tip; and a structure supporting the tip andsupporting an application of force to deform the tip conductive surface.2. The stylus of claim 1, wherein the structure is a conductive shaftcoupled to the tip.
 3. The stylus of claim 1, wherein the tip issemi-rigid.
 4. The stylus of claim 1, wherein the tip is made from ablend of conductive and non-conductive fibers.
 5. The stylus of claim 1,wherein the tip comprises conductive fibers and base fibers that havebeen felted with the conductive fibers.
 6. The stylus of claim 5,wherein the base fibers are wool fibers.
 7. The stylus of claim 5,wherein the conductive fibers are carbon fibers.
 8. The stylus of claim5, wherein the conductive fibers are fibers coated with metal.
 9. Thestylus of claim 5, wherein the conductive fibers are fibers coated withcarbon.
 10. The stylus of claim 5, wherein the conductive fibers haveelectrical resistivity such that the combined resistance and capacitanceof the tip, when the tip is coupled to the capacitance, in aggregate, issufficient to cause the capacitive touch screen to recognize a touch bythe tip, and the capacitance of the tip alone is insufficient to causethe capacitive touch screen to recognize a touch by the tip.
 11. Thestylus of claim 5, wherein the conductive fibers have electricalresistivity not more than on the order of 10,000,000 ohms-cm).
 12. Thestylus of claim 1, wherein the tip has an at least substantiallybullet-like shape when in an undeformed state.
 13. The stylus of claim1, wherein the tip has an at least substantially hemispherical shapewhen in an undeformed state.
 14. The stylus of claim 1, wherein thestructure includes a conductive shaft, and said stylus also includes:switched circuitry selectable to provide a configuration state thatforms a low impedance path that couples an additional amount ofcapacitance to the tip, the combined capacitance sufficient to allow thecapacitive touch screen to recognize a touch by the tip, and wherein theswitched circuitry in an alternate state does not couple to sufficientadditional capacitance to the tip to allow the capacitive touch screento recognize a touch by the tip.
 15. A system comprising: a capacitivetouch screen device comprising: a capacitive touch screen surface; acontroller that defines a touch event on the capacitive touch screensurface by the touch event having at least a threshold contact areavalue and a threshold change in local capacitance value; and, a styluscomprising: a tip with a conductive surface coupled to a capacitance,the tip and capacitance switchable from a first state in which the tipcoupled to the capacitance stimulates the capacitive touch screensurface to a second state in which the tip does not stimulate thecapacitive touch screen surface; and, support structure for supportingthe application of the stylus tip to the capacitive touch screensurface.
 16. The stylus of claim 15, wherein said tip is a felted tipthat includes base fibers and conductive fibers felted with the basefibers.
 17. The stylus of claim 15, wherein the tip coupled to thecapacitance is passively switchable between the first state and thesecond state.
 18. The stylus of claim 15, wherein the structure includesa conductive shaft, and said stylus also includes: switched circuitryselectable between the first state that forms a low impedance path thatcouples an additional amount of capacitance to the tip, the combinedcapacitance sufficient to allow the capacitive touch screen to recognizea touch by the tip, and wherein the switched circuitry in the secondstate does not couple to sufficient additional capacitance to the tip toallow the capacitive touch screen to recognize a touch by the tip. 19.The stylus of claim 18, wherein the switched circuitry also includes astylus audio port set, including at least one audio port configured tobe coupled to an audio cable.
 20. The stylus of claim 19, wherein thestylus audio port set includes at least one audio input port, and atleast one audio output port.
 21. The stylus of claim 19, wherein thestylus audio port set has a state indicative of contact between the tipand an object external to the stylus.
 22. The stylus of claim 19,wherein the stylus audio port set has a state indicative of pressureexerted by an object on the tip.
 23. The stylus of claim 19, wherein theswitched circuitry includes at least one sensor, and the stylus audioport set has a state indicative state of the sensor.
 24. The stylus ofclaim 19, wherein the stylus audio port set has a state indicative ofstate of at least one switch of the switched circuitry.
 25. The stylusof claim 19, wherein the audio cable includes left and right outputchannel connectors, a microphone channel connector, and a groundconnector, and the stylus audio port set is configured to be coupled toan end of the audio cable, such that another end of the cable can becoupled to a host audio port set of a capacitive touch screen device.26. In a system having a capacitive touch screen device comprising: acapacitive touch screen surface; a controller that defines a touch eventon the capacitive touch screen surface by the touch event having atleast a threshold contact area value and at least a threshold change inlocal capacitance value; and, a stylus comprising: a tip with aconductive surface coupled to a capacitance, the tip and capacitanceswitchable from a first state (tip down) in which the tip coupled to thecapacitance stimulates the capacitive touch screen surface to a secondstate (tip up) in which the tip does not stimulate the capacitive touchscreen surface, a method comprising: a) transmitting from the stylus tothe capacitive touch screen device, a signal associated with atransition in the stylus from the tip up state to the tip down state andassigning a time T1 to that signal; b) on the capacitive touch screendevice, gathering all touch event data, including touch events, if any,associated with contact between the stylus tip in the tip down state andthe capacitive touch screen; c) for gathered touch events that occurredwithin a predetermined time interval relative to T1, creating acollection of unclassified touch event data; and d) processing thecollected unclassified touch event data to differentiate touch eventslikely caused by movement of the stylus tip in the tip down state fromtouch events likely caused by touches of the capacitive touch screen byobjects other than the stylus.
 27. A stylus, including: tip with adeformable conductive surface; and switched circuitry having a firststate which couples additional capacitance to the tip, where thecombined capacitance is sufficient to cause a change in a local electricfield of a capacitive touch screen device sufficient to allow the deviceto recognize, as a touch, simple contact of the tip on of the capacitivetouch screen device, wherein the switched circuitry also has a secondstate which decouples the additional capacitance from the tip, and thecapacitance of the tip alone is insufficient to cause the capacitivetouch screen device to recognize a touch by the tip.
 28. The stylus ofclaim 27, wherein the conductive tip is a conductive, felted tip that isdeformable, and includes base fibers and conductive fibers felted withthe base fibers.
 29. The stylus of claim 27, wherein the switchedcircuitry is passive switched circuitry.
 30. The stylus of claim 27,wherein the capacitance is a capacitive load external to the stylus. 30.The stylus of claim 27, wherein the capacitance is internal to thestylus.
 31. The stylus of claim 27, wherein the switched circuitryincludes at least one switch biased in a default state which couples theadditional capacitance to the tip but is switchable in response tomovement of the tip into a second state which decouples the capacitancefrom said tip, where the switch is coupled to the tip in the defaultstate.
 32. The stylus of claim 27, wherein the switched circuitryincludes at least one switch biased in a default state which decouplesthe additional capacitance from the tip but is switchable in response tomovement of the tip into a second state which couples the additionalcapacitance to said tip, where the switch is coupled to the tip in thesecond state.
 33. The stylus of claim 27, wherein the switched circuitryalso includes a stylus audio port set, including at least one audio portconfigured to be coupled to an audio cable.
 34. The stylus of claim 27,wherein the switched circuitry includes at least one variable circuitelement whose state is determined by sensor input.
 35. The stylus ofclaim 34, wherein the switched circuitry also includes an audio portset, including at least one audio port configured to be coupled to anaudio cable, and the switched circuitry is configured to assert to theaudio port set a response signal indicative of state of the variablecircuit element.